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2012-06-30
|
Anticollinear magnetic order induced by impurities in the frustrated Heisenberg model of pnictides
|
We present Monte Carlo simulations for a classical antiferromagnetic
Heisenberg model with both nearest ($J_1$) and next-nearest ($J_2$) exchange
couplings on the square lattice in the presence of non-magnetic impurities. We
show that the order-by-disorder entropy selection, associated with the
Ising-like phase transition that appears for $J_2/J_1>1/2$ in the pure spin
model, is quenched at low temperature due to the presence of non-magnetic
impurities. Evidences that a new competing order is stabilized around the
impurities, and in turn induces a re-entrance phase transition are reported.
Implications for local magnetic measurement of the parent compound of iron
pnictides are briefly discussed.
|
1207.0095v1
|
2012-07-13
|
Theoretical study of the hyperfine field at Cu impurities diluted in an iron host
|
Magnetic hyperfine field at Cu isotopes as impurities in Fe were recently
measured at low temperature. A model to explain these experimental results is
proposed. The diluted Cu impurities in the ferromagnetic Fe host are described
by an extension of the Daniel-Friedel model, including the next neighbor
perturbation. In order to account for the available experimental data in Cu
isotopes with atomic masses $A$ = 59, 67, 69 and 71 as impurity, we needed to
incorporate the Cu anomaly volume in the effective charge to be screened and in
the self-consistent procedures.
|
1207.3327v1
|
2012-08-09
|
E906/SeaQuest MARS15 Simulation
|
A series of MARS15 simulations were done to verify and guide the design of
steel and concrete shielding, around the first E906-SeaQuest spectrometer
magnet, and the target area immediately upstream of it. The result of the last
round of simulations is summarized here. This magnet is a solid iron dipole
magnet and serves as a beam dump, as well as a muon analysis magnet.
The E906-SeaQuest spectrometer is designed to measure high energy muons
produced in the forward direction by interactions of the FNAL 120-GeV Main
Injector proton beam, with a variety of targets.
|
1208.1998v1
|
2012-08-17
|
Majorana Zero Modes in Semiconductor Nanowires in Contact with Higher-$T_c$ Superconductors
|
We analyze the prospects for stabilizing Majorana zero modes in semiconductor
nanowires that are proximity-coupled to higher-temperature superconductors. We
begin with the case of iron pnictides which, though they are s-wave
superconductors, are believed to have superconducting gaps that change sign. We
then consider the case of cuprate superconudctors. We show that a nanowire on a
step-like surface, especially in an orthorhombic material such as YBCO, can
support Majorana zero modes at an elevated temperature.
|
1208.3701v2
|
2012-09-16
|
Stabilization of STEP electrolyses in lithium-free molten carbonates
|
This communication reports on effective electrolyses in lithium-free molten
carbonates. Processes that utilize solar thermal energy to drive efficient
electrolyses are termed Solar Thermal Electrochemical Processes (STEP).
Lithium-free molten carbonates, such as a sodium-potassium carbonate eutectic
using an iridium anode, or a calcium-sodium-potassium carbonate eutectic using
a nickel anode, can provide an effective medium for STEP electrolyses. Such
electrolyses are useful in STEP carbon capture, and the production of staples
including STEP fuel, iron, and cement.
|
1209.3512v1
|
2012-09-17
|
Size and polydispersity effect on the magnetization of densely packed magnetic nanoparticles
|
The magnetic properties of densely packed magnetic nanoparticles (MNP)
assemblies are investigated from Monte Carlo simulations. The case of iron
oxide nanoparticles is considered as a typical example of MNP. The main focus
is put on particle size and size polydispersity influences on the magnetization
curve. The particles are modeled as uniformly magnetized spheres isolated one
from each other by a non magnetic layer representing the organic coating. A
comparison with recent experimental results on $\gamma-$Fe$_2$O$_3$ powder
samples differing by their size is given.
|
1209.3566v1
|
2012-10-01
|
Disc atmospheres and winds in X-ray binaries
|
We review the current status of studies of disc atmospheres and winds in low
mass X-ray binaries. We discuss the possible wind launching mechanisms and
compare the predictions of the models with the existent observations. We
conclude that a combination of thermal and radiative pressure (the latter being
relevant at high luminosities) can explain the current observations of
atmospheres and winds in both neutron star and black hole binaries. Moreover,
these winds and atmospheres could contribute significantly to the broad iron
emission line observed in these systems.
|
1210.0318v1
|
2012-10-09
|
Thermopower as sensitive probe of electronic nematicity in iron pnictides
|
We study the in-plane anisotropy of the thermoelectric power and electrical
resistivity on detwinned single crystals of isovalent substituted
EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_2$. Compared to the resistivity anisotropy the
thermopower anisotropy is more pronounced and clearly visible already at
temperatures much above the structural and magnetic phase transitions. Most
remarkably, the thermopower anisotropy changes sign below the structural
transition. This is associated with the interplay of two contributions due to
anisotropic scattering and orbital polarization, which dominate at high- and
low-temperatures, respectively.
|
1210.2634v2
|
2012-10-22
|
Holographic model of the S^{+/-} multiband superconductor
|
We construct the holographic model of an $S^\pm$ multiband superconductor.
This system is a candidate to explain the anomalous features of the iron-based
superconductors (e.g. LaFeAsO, BFe2As2, and other pnictides and arsenides). We
study the framework, which allows formation of the sign-interchanging order
parameter. We also calculate the electric AC conductivity and study its
features, related to the interband interaction.
|
1210.6074v3
|
2012-12-13
|
On the existence of solutions for a drift-diffusion system arising in corrosion modelling
|
In this paper, we consider a drift-diffusion system describing the corrosion
of an iron based alloy in a nuclear waste repository. In comparison with the
classical drift-diffusion system arising in the modeling of semiconductor
devices, the originality of the corrosion model lies in the boundary conditions
which are of Robin type and induce an additional coupling between the
equations. We prove the existence of a weak solution by passing to the limit on
a sequence of approximate solutions given by a semi-discretization in time.
|
1212.3279v1
|
2012-12-23
|
Excited nuclei in neutron star crusts
|
The paper considers the chains of successive electron capture reactions by
nuclei of the iron group which take place in the crystal structures of neutron
star envelopes. It is shown that as a result of such reactions the daughter
nuclei in excited states accumulate within certain layers of neutron star
crusts. The phonon model of interactions is proposed between the excited nuclei
in the crystalline structure, as well as formation of highly excited nuclear
states which emit neutrons and higher energy photons.
|
1212.5767v1
|
2012-12-23
|
Acausality of Massive Gravity
|
We show, by analyzing its characteristics, that the ghost-free, 5 degree of
freedom, Wess--Zumino massive gravity model admits superluminal shock wave
solutions and thus is acausal. Ironically, this pathology arises from the very
constraint that removes the (sixth) Boulware-Deser ghost mode.
|
1212.5835v3
|
2013-01-08
|
Normal and superconducting properties of LiFeAs explained in the framework of four-band Eliashberg Theory
|
In this paper we propose a model to reproduce superconductive and normal
properties of the iron pnictide LiFeAs in the framework of the four-band spm
wave Eliashberg theory. A confirmation of the multiband nature of the system
rises from the experimental measurements of the superconductive gaps and
resistivity as function of temperature. We found that the most plausible
mechanism is the antiferromagnetic spin fluctuation and the estimated values of
the total antiferromagnetic spin fluctuation coupling constant in the
superconductive and normal state are lambda{tot}=2.00 and lambda{tot,tr}=0.77.
|
1301.1542v1
|
2013-01-24
|
Pressure effects in hollow and solid iron oxide nanoparticles
|
We report a study on the pressure response of the anisotropy energy of hollow
and solid maghemite nanoparticles. The differences between the maghemite
samples are understood in terms of size, magnetic anisotropy and shape of the
particles. In particular, the differences between hollow and solid samples are
due to the different shape of the nanoparticles and by comparing both pressure
responses it is possible to conclude that the shell has a larger pressure
response when compared to the core.
|
1301.5708v1
|
2013-04-10
|
Normal state bottleneck and nematic fluctuations from femtosecond quasi-particle relaxation dynamics in Sm(Fe,Co)AsO
|
We investigate temperature and fluence dependent dynamics of the photoexcited
quasi-particle relaxation and low-energy electronic structure in electron-doped
1111-structure Sm(Fe_{0.93}Co_{0.07})AsO single crystal. We find that the
behavior is qualitatively identical to the 122-structure Ba(Fe,Co)_{2}As_{2}
including the presence of a normal state pseudogap and a marked 2-fold symmetry
breaking in the tetragonal phase that we relate to the electronic nematicity.
The 2-fold symmetry breaking appears to be a general feature of the electron
doped iron pnictides.
|
1304.2866v1
|
2013-04-26
|
Ferroelectricity from iron valence ordering in rare earth ferrites?
|
The possibility of multiferroicity arising from charge ordering in LuFe2O4
and structurally related rare earth ferrites is reviewed. Recent experimental
work on macroscopic indications of ferroelectricity and microscopic
determination of coupled spin and charge order indicates that this scenario
does not hold. Understanding the origin of the experimentally observed charge
and spin order will require further theoretical work. Other aspects of recent
research in these materials, such as geometrical frustration effects, possible
electric-field-induced transitions, or orbital order are also briefly treated.
|
1304.7255v1
|
2013-07-04
|
Molten Air -- A new, highest energy class of rechargeable batteries
|
This study introduces the principles of a new class of batteries,
rechargeable molten air batteries, and several battery chemistry examples are
demonstrated. The new battery class uses a molten electrolyte, are quasi
reversible, and have amongst the highest intrinsic battery electric energy
storage capacities. Three examples of the new batteries are demonstrated. These
are the iron, carbon and VB2 molten air batteries with respective intrinsic
volumetric energy capacities of 10,000, 19,000 and 27,000 Wh per liter.
|
1307.1305v1
|
2013-07-16
|
On the He burning phases of the Carina dSph
|
We performed a detailed comparison between predicted He burning phases and
multiband photometry of the Carina dwarf spheroidal galaxy. We found a good
agreement with the predictions computed assuming an {\alpha}-enhanced chemical
mixture, indicating a mean metallicity [Fe/H] ~ -1.8 with a raw observed
peak-to-peak spread in iron abundance of 0.4\pm0.2 dex.
|
1307.4324v1
|
2013-08-05
|
Sub-Piconewton Force Detection using Micron-Size Wire Deflections
|
The mechanical properties of nanostructured wires obtained by co-assembly of
iron oxide particles are studied. The intrinsic magnetic properties of the
wires are used to induce and quantify the bending of the one-dimensional
objects. From the relationship between the deflection and the magnitude of the
magnetic field, the elastic rigidity and Young modulus of the wires are
determined. Young moduli in the megapascal range are obtained and are
consistent with sub-piconewton force detection.
|
1308.0893v1
|
2013-08-13
|
Strain effects on electronic structure of the iron selenide superconductor
|
The influence of various strains on crystal and electronic structures of
superconducting FeSe has been studied ab initio. We consider changes in the
Fermi surface nesting with a vector Q=(0.5,0.5)*(2\pi /a) as crucial for rising
superconductivity (SC) mediated by spin-fluctuations (SF). Our results indicate
that the c-axis strained FeSe exhibits the most imperfect nesting, which
enhances SF and, hence, also SC. In turn, the ab-plane compressive strain
slightly weakens this} nesting while the tensile strain destroys it completely.
These findings are consistent with reported earlier experimental dependencies
of superconducting transition temperatures on strain in FeSe thin films.
|
1308.2933v1
|
2013-08-26
|
Modélisation micromagnétique du comportement magnéto-mécanique
|
A magneto-mechanical static modeling of ferromagnetic particle based on
minimization of an energy function is presented. This modeling is made of a
conjugate gradient method coupled with finite element method for the mechanical
problem resolution. Some illustrations on iron single crystal are given in 2D
framework.
|
1308.5494v1
|
2013-08-26
|
Sulfur annealing effect for superconductivity in iron chalcogenide compounds
|
We discovered a novel annealing method for Fe-chalcogenide superconductors.
It was found that sulfur annealing deintercalated excess Fe via formation of
FeS2. Due to its specifics, sulfur annealing is applicable when preparing
Fe-chalcogenide-based wires or cables.
|
1308.5642v1
|
2013-08-28
|
26Al in the Early Solar System: Not so Unusual After All
|
Recently acquired evidence shows that extrasolar asteroids exhibit over a
factor of 100 variation in the iron to aluminum abundance ratio. This large
range likely is a consequence of igneous differentiation that resulted from
heating produced by radioactive decay of 26Al with an abundance comparable to
that in the solar system's protoplanetary disk at birth. If so, the
conventional view that our solar system began with an unusually high amount of
26Al should be discarded.
|
1308.6325v2
|
2013-09-11
|
Investigating of longitudinal development parameters through air shower simulation by different hadronic models
|
In this work the simulation of the Extensive Air Showers was performed by
investigating the longitudinal development parameters (N and Xmax) by using a
system for air shower simulation which is called AIRES version 2.6.0 at the
energy range (10^14-10^19 eV) for different primary particles like (gamma,
electron, positron, proton and iron nuclei) and different zenith angles. The
comparison of simulated longitudinal profile was fulfilled for different
hadronic models (SIBYLL, QGSJET99 and SIBYLL S16).
|
1309.2934v1
|
2013-10-11
|
Impurity bound states and disorder-induced orbital and magnetic order in the s+- state of Fe-based superconductors
|
We study the presence of impurity bound states within a five-band Hubbard
model relevant to iron-based superconductors. In agreement with earlier
studies, we find that in the absence of Coulomb correlations there exists a
range of repulsive impurity potentials where in-gap states are generated. In
the presence of weak correlations, these states are generally pushed to the
edges of the gap, whereas for larger correlations the onsite impurity potential
induces a local magnetic region which reintroduces the low-energy bound states
into the gap.
|
1310.3022v1
|
2013-10-14
|
From quantum mechanics to the physical metallurgy of steels
|
In the last decade there has been a breakthrough in the construction of
theories leading to models for the simulation of atomic scale processes in
steel. In this paper the theory is described and developed and used to
demonstrate calculations of the diffusivity and trapping of hydrogen in iron
and the structures of carbon vacancy complexes in steel.
|
1310.3778v3
|
2013-11-13
|
A DFT+Nonhomogeneous DMFT approach for Finite Systems
|
For reliable and efficient inclusion of electron-electron correlation effects
in nanosystems we propose a combined density-functional-theory/nonhomogeneous
dynamical-mean-field-theory (DFT + DMFT) approach which employs an approximate
Iterative Perturbative Theory (IPT) impurity solver. The validity of the method
is demonstrated by successful examination of the size-dependent magnetic
properties of iron nanoparticles containing 11-100 atoms. We show that the DFT+
DMFT solution is in very good agreement with experimental data, in particular
it does not lead to the overestimation of magnetization that is found with the
DFT and DFT+U techniques. More importantly, we demonstrate that DFT+DMFT
approach can be used for accurate and realistic description of nanosystems
containing about hundred atoms.
|
1311.3147v1
|
2014-01-10
|
A density functional theory study of FeAs comparing LDA+U, GGA+U and hybrid functionals
|
We use density functional theory within the local density approximation
(LDA), LDA+U, generalized gradient approximation (GGA), GGA+U, and
hybrid-functional methods to calculate the properties of iron monoarsenide.
FeAs, which forms in the MnP structure, is of current interest for potential
spintronic applications as well as being the parent compound for the
newly-identified pnictide superconductors. We compare the calculated
structural, magnetic and electronic properties obtained using the different
functionals to each other and to experiment, and investigate the origin of a
recently-reported magnetic spiral. Our results indicate the appropriateness or
otherwise of the various functionals for describing FeAs and the related
Fe-pnictide superconductors.
|
1401.2277v1
|
2014-03-19
|
Spin-orbit coupling effects on spin-dependent inelastic electronic lifetimes in ferromagnets
|
For the 3d ferromagnets iron, cobalt and nickel we compute the spin-dependent
inelastic electronic lifetimes due to carrier-carrier Coulomb interaction
including spin-orbit coupling. We find that the spin-dependent
density-of-states at the Fermi energy does not, in general, determine the spin
dependence of the lifetimes because of the effective spin-flip transitions
allowed by the spin mixing. The majority and minority electron lifetimes
computed including spin-orbit coupling for these three 3-d ferromagnets do not
differ by more than a factor of 2, and agree with experimental results.
|
1403.4728v1
|
2014-03-19
|
Topological Phases in the Single-Layer FeSe
|
A distinct electronic structure was observed in the single-layer FeSe which
shows surprising high temperature superconductivity over 65k. Here we
demonstrate that the electronic structure can be explained by the strain effect
due to substrates. More importantly, we find that this electronic structure can
be tuned into robust topological phases from a topologically trivial metallic
phase by the spin-orbital interaction and couplings to substrates. The
topological phase is robust against any perturbations that preserve the
time-reversal symmetry. Our studies suggest that topological phases and
topologically related properties such as Majorana Fermions can be realized in
iron-based high T$_{c}$ superconductors.
|
1403.4740v1
|
2014-05-23
|
New observations of chemically peculiar stars with ESPaDOnS
|
We present the first results of the estimation of gravity and effective
temperature for some poorly studied chemically peculiar stars that were
recently observed with the spectropolarimeter ESPaDOnS at CFHT. We have
analyzed the spectra of HD71030, HD95608 and HD116235 to determine their radial
velocity, Vsin(i) and the average abundance of several chemical species. We
have also analyzed our results to verify for possible vertical abundance
stratification of iron and chromium in these stars.
|
1405.6203v1
|
2014-06-12
|
A Simple Apparatus for the Direct Measurement of Magnetic Forces and Magnetic Properties of Materials
|
In this paper, we describe a simple apparatus consisting of a scale, capable
of a one milligram resolution, and a commonly obtainable magnet to measure
magnetic forces. This simple apparatus is capable of measuring magnetic
properties of materials in either a research or an instructional laboratory. We
illustrate the capability of this apparatus by the measurement of the force of
iron samples exerted on the magnet, the force of a paramagnetic sample, that by
a current carrying wire, and the force of a high temperature superconductor.
|
1406.3341v3
|
2014-06-15
|
Magnetotransport studies of FeSe under hydrostatic pressure
|
The discoveries of iron-based superconductors with relatively high transition
temperature are under intense experimental and theoretical investigation. Here
we present magnetotransport measurements on FeSe superconductor under
hydrostatic pressure. We show that in Fe-deficient tetragonal FeSe binary
compound, the onset of superconducting transition is almost doubled under
1.98GPa pressure and the estimated upper critical field of 26.7Tesla is
increased to 47.5Tesla.
|
1406.3795v2
|
2014-06-29
|
Specific Heat of Ca0.33Na0.67Fe2As2
|
The specific heat of single crystal hole-doped Ca0.33Na0.67Fe2As2,
Tc(onset)=33.7 K, was measured from 0.4 to 40 K. The discontinuity in the
specific heat at Tc, deltaC, divided by Tc is 105 +- 5 mJ/molK2, consistent
with values found previously for hole-doped Ba0.6K0.4Fe2As2 and somewhat above
the general trend for deltaC/Tc vs Tc for the iron based superconductors
established by Bud'ko, Ni and Canfield. The usefulness of measured valued of
deltaC/Tc as an important metric for the quality of samples is discussed.
|
1406.7519v1
|
2014-06-30
|
Primary Beam Steering Due to Field Leakage from Superconducting SHMS Magnets
|
Simulations of the magnetic fields from the Super High Momentum Spectrometer
in Hall C at Thomas Jefferson National Accelerator Facility show significant
field leakage into the region of the primary beam line between the target and
the beam dump. Without mitigation, these remnant fields will steer the
unscattered beam enough to limit beam operations at small scattering angles.
Presented here are magnetic field simulations of the spectrometer magnets and a
solution using optimal placement of a minimal amount of shielding iron around
the beam line.
|
1406.7856v2
|
2014-07-13
|
Investigation on mass composition of UHE cosmic rays using CRPropa 2.0
|
In this paper, we used the Monte Carlo code CRPropa version 2.0 to simulate
the propagation of UHE cosmic rays. In the simulation, uniform cosmic ray
sources with spectral indices of {\alpha} = 1.4, {\alpha} = 2 and Emax = 1021
eV for pure iron composition at the source position are assumed. We obtained
the logarithmic average mass of cosmic rays as a function of energy and
compared it with the experimental values in the ankle, and we demonstrated how
the mass composition changes before and after the ankle.
|
1407.3468v1
|
2014-07-18
|
Superconductivity in FeTe{1-x}S_x induced by electrochemical reaction using ionic liquid solution
|
Superconductivity in FeTe0.8S0.2 is successfully induced by an
electrochemical reaction using an ionic liquid solution. A clear correlation
between the Fe concentration in the solution and the manifestation of
superconductivity was confirmed, suggesting that superconductivity was induced
by the deintercalation of excess iron.
|
1407.4932v1
|
2014-07-22
|
Femtosecond intrapulse evolution of the magneto-optic Kerr effect in magnetoplasmonic crystals
|
In magnetoplasmonics, it is possible to tailor the magneto-optical properties
of nanostructures by exciting surface plasmon polaritons (SPPs). Thus far,
magnetoplasmonic effects have been considered static. Here, we describe
ultrafast manifestations of magnetoplasmonics by observing the non-trivial
evolution of the transverse magneto-optic Kerr effect within 45-fs pulses
reflected from an iron-based magnetoplasmonic crystal. The effect occurs for
resonant SPP excitations, displays opposite time derivative signs for different
slopes of the resonance, and is explained with the magnetization-dependent
dispersion relation of SPPs.
|
1407.5845v1
|
2014-07-28
|
Minimal model of point contact Andreev reflection spectroscopy of multiband superconductors
|
We formulate a minimal model of point contact Andreev reflection spectroscopy
of a normal- metal/multiband superconductor interface. The theory generalizes
the Blonder-Tinkham-Klapwijk (BTK) formulation to a multiband superconductor
and it is based on the quantum waveguides theory. The proposed approach allows
an analytic evaluation of the Andreev and normal reflection coefficients and
thus is suitable for a data fitting of point contact experiments. The obtained
differential conductance curves present distinctive features similar to the
ones measured in the experiments on multiband systems, like the iron-based
pnictides and the MgB2.
|
1407.7397v1
|
2014-06-18
|
Artificial_Micrometeorites
|
An iron ball, a beryllium sphere and a tungsten tube segment with diameter
twenty microns, are electrically charged while proton beam irradiating. These
bodies are accelerated by the running pulse field in a spiral waveguide up to
velocity: thirty kilometers per second. The accelerator, generating
micrometeorites is placed at satellites on the Earth orbit. This article
considers processes of penetration of micrometeorites into the Earth
atmosphere. It is shown that micrometeorites evaporate at the height of one
hundred kilometers-one hundred fifty kilometers from the surface of the Earth.
A micrometeorite which is a segment of the beryllium tube equipped with a
graphite cone in the head part is the very meteorite to reach the Earth surface
without being broken.
|
1407.8542v1
|
2014-08-10
|
Growth of (NaxKy)FezSe2 crystals by chlorides flux at low temperatures
|
(NaxKy)FezSe2 crystals are prepared by Na, Fe, and Se as starting materials
in NaCl/KCl flux at low temperatures~720 {\deg}C. It is found that K is more
preferred than Na to enter in between FeSe layers and forms the phase.
Thus-obtained crystals contain more superconducting phase in volume fraction
and exhibit new features in transport property. Our results provide a promising
new synthetic route for preparing quality crystals of iron selenide
superconductors.
|
1408.2181v1
|
2014-09-16
|
X-ray Filament with a Strong 6.7 keV Line in the Galactic Center Region
|
An elongated X-ray source with a strong K-shell line from He-like iron (Fe
XXVI) is found at (RA, Dec)_{J2000.0}=(17h44m00s.0, -29D13'40''.9) in the
Galactic center region. The position coincides with the X-ray thread,
G359.55+0.16, which is aligned with the radio non-thermal filament. The X-ray
spectrum is well fitted with an absorbed thin thermal plasma (apec) model. The
best-fit temperature, metal abundance, and column density are 4.1^{+2.7}_{-1.8}
keV, 0.58^{+0.41}_{-0.32} solar, and 6.1^{+2.5}_{-1.3}x10^{22} cm^{-2},
respectively. These values are similar to those of the largely extended
Galactic center X-ray emission.
|
1409.4520v1
|
2014-09-22
|
Local magnetization nucleated by non-magnetic impurities in Fe-based superconductors
|
We study impurity-induced magnetic order within a five-band Hubbard model
relevant to the normal paramagnetic phase of iron-based superconductors. The
existence of the local magnetic order is explained in terms of an
impurity-enhancement of states near the Fermi level, and we map out the
resulting phase diagram of the existence of magnetization as a function of
impurity strength and Coulomb correlations. In particular, the presence of
impurity-induced magnetism in only a certain range of potential scattering
strengths can be understood from the specific behavior of the impurity resonant
state.
|
1409.6068v1
|
2014-10-06
|
Analysis of point contact spectra of kfe2as2 in the thermal regime
|
The point-contact spectra of the iron-based compound KFe2As2 were analyzed
according to the thermal regime theory. We have obtained the values of the
residual resistivity, the Lorentz number, and the electron mean free path in
the contacts. It was shown that the most point-contact spectra can be described
by this theory. The reasons for this behavior are discussed.
|
1410.1322v1
|
2014-10-21
|
Concentrator of elastic waves
|
This article is dedicated to an opportunity of concentrating elastic waves in
the iron and water cones on the square of the cone vertex of the order of one
square centimeter. The square of the base of the cone is equal to one square
meter, its height one meter. The calculations assume that the cone hexogen
network lying in the cone basis explodes during the time of one microsecond and
causes an explosive wave converging to the vertex of the cone. It is shown that
this explosive wave can accelerate the body having a mass of three grams to
speed five kilometers per second.
|
1410.5537v1
|
2014-11-08
|
Ab-initio theory of Iron based superconductors
|
We report the first-principles study of superconducting critical temperature
and superconducting properties of Fe-based superconductors taking into account
on the same footing phonon, charge and spin-fluctuation mediated Cooper
pairing. We show that in FeSe this leads to a modulated s$\pm$ gap symmetry,
and that the antiferromagnetic paramagnons are the leading mechanism for
superconductivity in FeSe, overcoming the strong repulsive effect of both
phonons and charge pairing.
|
1411.2121v1
|
2014-11-16
|
Replica-exchange Wang-Landau sampling: Pushing the limits of Monte Carlo simulations in materials sciences
|
We describe the study of thermodynamics of materials using replica-exchange
Wang-Landau (REWL) sampling, a generic framework for massively parallel
implementations of the Wang-Landau Monte Carlo method. To evaluate the
performance and scalability of the method, we investigate the magnetic phase
transition in body-centered cubic (bcc) iron using the classical Heisenberg
model parametrized with first principles calculations. We demonstrate that our
framework leads to a significant speedup without compromising the accuracy and
precision and facilitates the study of much larger systems than is possible
with its serial counterpart.
|
1411.4212v1
|
2015-01-28
|
Magnetic Design of Superconducting Magnets
|
In this paper we discuss the main principles of magnetic design for
superconducting magnets (dipoles and quadrupoles) for particle accelerators. We
give approximated equations that govern the relation between the
field/gradient, the current density, the type of superconductor (Nb-Ti or
Nb3Sn), the thickness of the coil, and the fraction of stabilizer. We also
state the main principle controlling the field quality optimization, and
discuss the role of iron. A few examples are given to show the application of
the equations and their validity limits.
|
1501.07149v1
|
2015-01-31
|
Calculation of the specific heat of optimally K-doped BaFe$_2$As$_2$
|
The calculated specific heat of optimally K-doped BaFe$_2$As$_2$ in density
functional theory is about five times smaller than that found in the
experiment. We report that by adjusting the potential on the iron atom to be
slightly more repulsive for electrons improves the calculated heat capacity as
well as the structural, magnetic, and electronic properties of
Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$. Applying the same correction to the
antiferromagnetic state, we find that the electron-phonon coupling is strongly
enhanced.
|
1502.00055v2
|
2015-04-20
|
Orbital-lattice coupling and orbital ordering instability in iron pnictides
|
Orbital-ordering instability arising due to the intrapocket nesting is
investigated for the tight-binding models of pnictides in the presence of
orbital-lattice coupling. The incommensurate instabilities with small momentum,
which may play an important role in the nematic-ordering transition, vary from
model to model besides being more favorable in comparison to the spin-density
wave instability in the absence of good interpocket nesting. We also examine
the doping dependence of such instabilities. The electron-phonon coupling
parameter required to induce them are compared with the first-principle
calculations.
|
1504.04915v1
|
2015-05-12
|
Unified picture for the colossal thermopower compound FeSb$_2$
|
We identify the driving mechanism of the gigantic Seebeck coefficient in
FeSb$_2$ as the phonon-drag effect associated with an in-gap density of states
that we demonstrate to derive from excess iron. We accurately model electronic
and thermoelectric transport coefficients and explain the so far ill-understood
correlation of maxima and inflection points in different response functions.
Our scenario has far-reaching consequences for attempts to harvest the
spectacular powerfactor of FeSb$_2$.
|
1505.02946v1
|
2015-05-26
|
Violation of the Wiedemann-Franz law as an evidence of the pseudogap in the iron-based superconductor Ba(Fe1-xCox)2As2
|
Longitudinal and transverse transport coefficients of the Ba(Fe1-xCox)2As2
single crystals with x = 0, 0.045, 0.06 and 0.244 were measured in the
temperature range 1.4 - 300 K and in magnetic fields up to 12.5 T. The
resulting data were used to determine the temperature dependence of the Hall
Lorenz number (Lxy) and its evolution with doping. Lxy is defined by the
electronic contributions to the thermal and electrical conductivities and it is
found to differ from its canonical behavior. This shows the emergence of a
pseudogap in samples at intermediate doping.
|
1505.06993v1
|
2015-06-09
|
Convergence of a Finite Volume Scheme for a Corrosion Model
|
In this paper, we study the numerical approximation of a system of partial
dif-ferential equations describing the corrosion of an iron based alloy in a
nuclear waste repository. In particular, we are interested in the convergence
of a numerical scheme consisting in an implicit Euler scheme in time and a
Scharfetter-Gummel finite volume scheme in space.
|
1506.02996v1
|
2015-06-12
|
Predicting Unconventional High Temperature Superconductors in Trigonal Bipyramidal Coordinations
|
Cuprates and iron-based superconductors are two classes of unconventional
high Tc superconductors based on 3d transition elements. Recently, two
principles, correspondence principle and magnetic selective pairing rule, have
been emerged to unify their high Tc superconducting mechanisms. These
principles strongly regulate electronic structures that can host high Tc
superconductivity. Guided by these principles, here we propose high Tc
superconducting candidates that are formed by cation-anion trigonal bipyramidal
complexes with a d^7 filling configuration on the cation ions. Their
superconducting states are expected to be dominated by the d+id pairing
symmetry.
|
1506.03904v2
|
2015-08-06
|
Time-reversal symmetry breaking state in dirty three-band superconductor
|
I study the effects of disorder on the superconductivity of a three-band
model with repulsive interband pairing. Such a model can support several
possible superconducting order parameters, including a complex time-reversal
symmetry breaking (TRSB) state. Impurity scattering suppresses the critical
temperature of all these states, but the complex state survives, and remains a
part of the phase diagram of the model even in the presence of moderate amount
of disorder. This means that the TRSB states could be experimentally accessible
in multiband materials like iron pnictides and chalcogenides.
|
1508.01517v1
|
2015-09-14
|
A Practioner's Guide to Evaluating Entity Resolution Results
|
Entity resolution (ER) is the task of identifying records belonging to the
same entity (e.g. individual, group) across one or multiple databases.
Ironically, it has multiple names: deduplication and record linkage, among
others. In this paper we survey metrics used to evaluate ER results in order to
iteratively improve performance and guarantee sufficient quality prior to
deployment. Some of these metrics are borrowed from multi-class classification
and clustering domains, though some key differences exist differentiating
entity resolution from general clustering. Menestrina et al. empirically showed
rankings from these metrics often conflict with each other, thus our primary
motivation for studying them. This paper provides practitioners the basic
knowledge to begin evaluating their entity resolution results.
|
1509.04238v1
|
2015-09-15
|
Lambda Boo Abundance Patterns: Accretion from Orbiting Sources
|
The abundance anomalies in lambda Boo stars are popularly explained by
element-specific mass inflows at rates that are much greater than
empirically-inferred bounds for interstellar accretion. Therefore, a lambda Boo
star's thin outer envelope must derive from a companion star, planet, analogs
to Kuiper Belt Objects or a circumstellar disk. Because radiation pressure on
gas-phase ions might selectively allow the accretion of carbon, nitrogen, and
oxygen and inhibit the inflow of elements such as iron, the source of the
acquired matter need not contain dust. We propose that at least some lambda Boo
stars accrete from the winds of hot Jupiters.
|
1509.04672v2
|
2015-09-20
|
Antimatter in the Direct-Action Theory of Fields
|
One of Feynman's greatest contributions to physics was the interpretation of
negative energies as antimatter in quantum field theory. A key component of
this interpretation is the Feynman propagator, which seeks to describe the
behavior of antimatter at the virtual particle level. Ironically, it turns out
that one can dispense with the Feynman propagator in a direct-action theory of
fields, while still retaining the interpretation of negative energy solutions
as antiparticles.
|
1509.06040v1
|
2015-10-07
|
Electromagnetically controlled multiferroic thermal diode
|
We propose an electromagnetically tunable thermal diode based on a two phase
multiferroics composite. Analytical and full numerical calculations for
prototypical heterojunction composed of Iron on Barium titanate in the
tetragonal phase demonstrate a strong heat rectification effect that can be
controlled externally by a moderate electric field. This finding is of an
importance for thermally based information processing and sensing and can also
be integrated in (spin)electronic circuits for heat management and recycling.
|
1510.02058v1
|
2015-10-29
|
New intercalation superconductor Lix(C6H16N2)yFe2-zSe2 with a very large interlayer-spacing and Tc = 38 K
|
A new iron-based superconductor, Lix(C6H16N2)yFe2-zSe2, with Tc = 38 K has
successfully been synthesized via the intercalation of lithium and
hexamethylenediamine into FeSe. The superconducting transition has been
confirmed not only by magnetic susceptibility measurements but also by
electrical resistivity ones. The interlayer spacing, namely, the dicstance
between neighboring Fe layers, d, is 16.225(5) $\mathring{\text{A}}$, which is
the largest among those of FeSe-based intercalation compounds. It has been
found that the dependence of Tc on d in FeSe-based intercalation
superconductors appears domic.
|
1510.08625v1
|
2015-10-29
|
First-principles study of FeSe epitaxial films on SrTiO3
|
The discovery of high temperature superconductivity in FeSe films on SrTiO3
substrate has inspired great experimental and theoretical interests.
First-principles density functional theory calculations, which have played an
important role in the study of bulk iron-based superconductors, also
participate in the investigation of interfacial superconductivity. In this
article, we review the calculation results on the electronic and magnetic
structures of FeSe epitaxial films, emphasizing on the interplay between
different degrees of freedom, such as charge, spin, and lattice vibrations.
Furthermore, the comparison between FeSe monolayer and bilayer films on SrTiO3
is discussed.
|
1510.08630v1
|
2015-11-10
|
Slow in-plane magnetoresistance oscillations in multiband quasi-two-dimensional metals
|
Slow oscillations (SlO) of magnetoresistance is a convenient tool to measure
electronic structure parameters in quasi-two-dimensional metals. We study the
possibility to apply this method to multi-band conductors, e.g. to iron-based
high-temperature superconducting materials. We show that SlO can be used to
measure the interlayer transfer integral in multi-band conductors similar to
single-band metals. In addition, the SlO allow to measure and compare the
effective masses or the electron scattering rates in various bands.
|
1511.03178v1
|
2015-11-16
|
Mixture model of pottery distributions from Lake Chad Basin archaeological sites reveals ancient segregation patterns
|
We present a new statistical approach to analyzing an extremely common
archaeological data type -- potsherds -- that infers the structure of cultural
relationships across a set of excavations. This method, applied to data from a
set of complex, culturally heterogeneous sites around the Mandara mountains in
the Lake Chad Basin, articulates currently understood cultural succession into
the Iron Age. We show how the approach can be integrated with radiocarbon dates
to provide detailed portraits of cultural dynamics and deposition patterns
within single excavations that, in this context, indicate historical
ethnolinguistic segregation patterns. We conclude with a discussion of the many
possible model extensions using other archaeological data types.
|
1511.05185v1
|
2015-12-17
|
Point defect absorption by grain boundaries in $α$-iron by atomic density function modeling
|
Using the atomic density function theory (ADFT), we examine the point defect
absorption at [110] symmetrical tilt grain boundaries in body-centered cubic
iron. It is found that the sink strength strongly depends on misorientation
angle. We also show that the ADFT is able to reproduce reasonably well the
elastic properties and the point defect formation volume in $\alpha$-iron.
|
1512.05492v1
|
2016-01-14
|
Giant domain wall response of highly twinned ferroelastic materials
|
Many ferroelastic crystals display at sufficiently low measurement
frequencies a huge elastic softening below Tc which is caused by domain wall
motion. Materials range from perovskites to iron based superconductors and
shape memory materials. We present a model - based on Landau-Ginzburg theory
including long range elastic interaction between needle shaped ferroelastic
domains - to describe the observed superelastic softening. The theory predicts
that the domain wall contribution to the elastic susceptibility is different
for improper and proper ferroelastic materials. A test of the theory against
experimental data on SrTiO3, KMnF3, LaAlO3, La1-xNdxP5O14 and NH4HC2O4.1/2H2O
yields excellent agreement.
|
1601.03590v1
|
2016-01-25
|
Influence of Lifshitz transitions and correlation effects on the scattering rates of the charge carriers in iron-based superconductors
|
Minimum model calculations on the co-action of hole vanishing Lifshitz
transitions and correlation effects in ferropnictides are presented. The
calculations predict non-Fermi-liquid behaviour and huge mass enhancements of
the charge carriers at the Fermi level. The findings are compared with recent
ARPES experiments and with measurements of transport and thermal properties of
ferropnictides. The results from the calculation can be also applied to other
unconventional superconductors and question the traditional view of quantum
critical points.
|
1601.06516v1
|
2016-02-01
|
A Short Note on Improved Logic Circuits in a Hexagonal Minesweeper
|
This paper aims to present an advanced version of PP-hardness proof of
Minesweeper by Bondt. The advancement includes improved Minesweeper
configurations for 'logic circuits' in a hexagonal Minesweeper. To do so, I
demonstrate logical uncertainty in Minesweeper, which ironically allows a
possibility to make some Boolean operators.
The fact that existing hexagonal logic circuits did not clearly distinguish
the true and false signal needs an improved form of a hexagonal wire. I
introduce new forms of logic circuits such as NOT, AND, OR gates, a curve and a
splitter of wires. Moreover, these new logic circuits complement Bondt's proof
for PP-hardness of Minesweeper by giving a new figure.
|
1602.00398v1
|
2016-03-10
|
First-Principles Momentum-Dependent Local Ansatz Wavefunction and Momentum Distribution Function Bands of Iron
|
We have developed a first-principles local ansatz wavefunction approach with
momentum-dependent variational parameters on the basis of the tight-binding
LDA+U Hamiltonian. The theory goes beyond the first-principles Gutzwiller
approach and quantitatively describes correlated electron systems. Using the
theory, we find that the momentum distribution function (MDF) bands of
paramagnetic bcc Fe along high-symmetry lines show a large deviation from the
Fermi-Dirac function for the $d$ electrons with $e_{g}$ symmetry and yield the
momentum-dependent mass enhancement factors. The calculated average mass
enhancement $m^{\ast}/m = 1.65$ is consistent with low-temperature specific
heat data as well as recent angle-resolved photoemission spectroscopy (ARPES)
data.
|
1603.03118v1
|
2016-03-19
|
Magnetic behaviour of dirty multiband superconductors near the upper critical field
|
Magnetic properties of dirty multiband superconductors near the upper
critical field are studied. The parameter $\kappa_2$ characterizing
magnetization slope is shown to have a significant temperature variation which
is quite sensitive to the pairing interactions and relative strengths of
intraband impurity scattering. In contrast to single-band superconductors the
increase of $\kappa_2$ at low temperatures can be arbitrary large determined by
the ratio of minimal and maximal diffusion coefficients in different bands.
Temperature dependencies of $\kappa_2(T)$ in two-band MgB$_2$ and iron-based
superconductors are shown to be much more sensitive to the multiband effects
than the upper critical field $H_{c2}(T)$.
|
1603.06054v1
|
2016-03-23
|
Large Magnetoresistance at Room Temperature in Ferromagnet/Topological Insulator Contacts
|
We report magnetoresistance for current flow through iron/topological
insulator (Fe/TI) and Fe/evaporated-oxide/TI contacts when a magnetic field is
used to initially orient the magnetic alignment of the incorporated
ferromagnetic Fe bar, at temperatures ranging from 100 K to room temperature.
This magnetoresistance is associated with the relative orientation of the Fe
bar magnetization and spin-polarization of electrons moving on the surface of
the TI with helical spin-momentum locking. The magnitude of the observed
magnetoresistance is relatively large compared to that observed in prior work.
|
1603.07283v1
|
2016-04-11
|
Doubling of the critical temperature of FeSe observed in point contacts
|
Rise in superconducting critical temperature Tc more than two times
(exceeding 20 K) is discov- ered in point-contacts created between
iron-chalcogenide FeSe single crystal and Cu. The possible reasons of such Tc
increase in point-contacts are discussed. The most probable cause for this may
be the interfacial carriers doping and/or interfacial enhanced electron-phonon
interaction.
|
1604.02921v2
|
2016-04-04
|
The Fine Structure Constant and Habitable Planets
|
We use the existence of habitable planets to impose anthropic requirements on
the fine structure constant, $\alpha$. To this effect, we present two
considerations that restrict its value to be very near the one observed. The
first, that the end product of stellar fusion is iron and not one of its
neighboring elements, restricts $\alpha^{-1}$ to be $145\pm 50$. The second,
that radiogenic heat in the Earth's interior remains adequately productive for
billions of years, restricts it to be $145\pm9$. A connection with the grand
unified theory window is discussed, effectively providing a route to probe
ultra-high energy physics with upcoming advances in planetary science.
|
1604.03151v1
|
2016-04-15
|
Electron magnetic resonance in magnetic nanoparticles: dependence on the particle size and applicability of the modified giant spin model
|
Superparamagnetic nanoparticles containing hundreds and thousands of coupled
electron spins are on the boundary between classical and quantum behavior, and
demonstrate features which are typical for paramagnetic spins and absent in
macroscopic ferromagnetic systems. In order to better understand the evolution
of magnetization dynamics from quantum to classical behavior with the increase
in the system size, we study the electron magnetic resonance signal in
suspensions of iron oxide nanoparticles as the function of the particle size.
The experimental data are compared with numerical simulations based on the
giant spin approach.
|
1604.04594v2
|
2016-04-21
|
Non-equilibrium magnetic fields in ab initio spin dynamics
|
Starting from the continuity equation for the magnetization in time-dependent
spin-density functional theory, we derive an expression for the effective
time-dependent magnetic fields driving the out-of-equilibrium spin dynamics in
magnetic systems. We evaluate these, so called, kinetic magnetic fields in the
ultrafast demagnetization response to optical pulse excitations of
ferromagnetic iron-based materials, namely Fe$_6$ cluster and bulk bcc Fe. We
identify spatial "hot spots" where the demagnetization is particularly enhanced
as a result of the increased kinetic torque.
|
1604.06262v2
|
2016-05-02
|
Study of glass properties as electrode for RPC
|
Operation and performance of the Resistive Plate Chambers (RPCs) mostly
depend on the quality and characteristics of the electrode materials. The
India-based Neutrino Observatory collaboration has chosen glass RPCs as the
active detector elements for its Iron Calorimeter detector and is going to
deploy RPCs in an unprecedented scale. Therefore, it is imperative that we
study the electrode material aspects in detail. We report here, systematic
characterization studies on the glasses from two manufacturers. RPC detectors
were built using these glasses and performances of the same were compared with
their material properties.
|
1605.01044v1
|
2016-05-07
|
Effect of glass thickness variations on the performance of RPC detectors
|
The India-based Neutrino Observatory (INO) is planning to build a magnetized
iron calorimeter detector (ICAL) in which Resistive Plate Chambers (RPCs) will
be the active detector elements. A study of the performance of RPCs, made using
electrodes of various thicknesses, is pivotal in optimizing the design
parameters of the ICAL RPCs. We fabricated RPCs with glasses of various
thicknesses and studied their performance in the same environmental conditions.
A study of detector efficiency, noise rate, time resolution and charge
distribution is presented in this paper.
|
1605.02189v2
|
2016-06-11
|
Hydrodynamics of Domain Walls in Multiferroics: Impact on Memory Devices
|
We show that switching in ferroelectric lead germanate and lead iron
tantalate zirconate titanate (PZTFT) does not resemble the equilibrium domain
structure evolution of the Landau-Lifshitz-Kittel model but is instead highly
nonequilibrium and similar, respectively, to the Richtmyer-Meshkov instability
in liquids and the Helfrich-Hursault sliding instability in liquid crystals.
The resulting nano-domain structures in PZTFT are circular or parabolic and
involving folding bifurcations. These may have an undesirable impact on
ferroelectric thin-film memoriesthat are also ferroelastic.
|
1606.03586v1
|
2016-06-12
|
Validity of the Local Approximation in Iron- Pnictides and Chalcogenides
|
We introduce a cluster DMFT (Dynamical Mean Field Theory) approach to study
the normal state of the iron pnictides and chalcogenides. In the regime of
moderate mass renormalizations, the self-energy is very local, justifying the
success of single site DMFT for these materials and for other Hunds metals. We
solve the corresponding impurity model with CTQMC (Continuous Time Quantum
Monte-Carlo) and find that the minus sign problem is not severe in regimes of
moderate mass renormalization.
|
1606.03660v1
|
2016-06-16
|
Three-dimensional Critical Dirac semimetal in KMgBi
|
We predicted that AMgBi (A=K,Rb Cs), which have the same lattice structures
as the 111 family of iron-based superconductors (Na/LiFeAs), are
symmetry-protected Dirac semimetals located near the boundary of type-I and
type-II Dirac semimetal phases. Doping Rb or Cs into KMgBi can drive the
transition between the two phases. The materials can also be turned into Weyl
semimetals and topological insulators by explicitly or spontaneously breaking
time-reversal symmetry and C$_4$ lattice symmetry respectively.
|
1606.05042v2
|
2016-06-23
|
Understanding doping, vacancy, lattice stability and superconductivity in KxFe2-ySe2
|
Metal-intercalated iron selenides are a class of superconductors that have
received much attention but are less understood in comparison with their
FeAs-based counterparts. Here, the controversial issues such as Fe vacancy, the
real phase responsible for superconductivity, and lattice stability have been
addressed based on first-principles calculations. New insights into the
distinct features in terms of carrier doping have been revealed.
|
1606.07217v1
|
2016-08-03
|
Compressive deformation of Fe nanopillar : Modalities of dislocation dynamics
|
Unlike the tensile mode, compressive deformation of a bcc metallic
nanostructure is mediated by the glide of screw dislocation. Although the bcc
screw dislocations are well known to possess unusual attributes, it is still
unclear how these unique effects manifest in a nanoscale solid. In the present
study, atomistic simulations render a close look at the dislocation activities
underlying the compressive deformation of bcc iron nanopillars. It is found
that instead of performing simple glide motion, the line defects exhibit a host
of complex features. In this regard, the temperature is observed to have a
pronounced effect on the dislocation mechanisms and consequently, on the
overall plastic response of the material. Additionally, statistical features of
the load-strain data have been explored.
|
1608.01166v1
|
2016-08-07
|
Spin-orbit coupling in Fe-based superconductors
|
We study the spin resonance peak in recently discovered iron-based
superconductors. The resonance peak observed in inelastic neutron scattering
experiments agrees well with predicted results for the extended $s$-wave
($s_\pm$) gap symmetry. Recent neutron scattering measurements show that there
is a disparity between longitudinal and transverse components of the dynamical
spin susceptibility. Such breaking of the spin-rotational invariance in the
spin-liquid phase can occur due to spin-orbit coupling. We study the role of
the spin-orbit interaction in the multiorbital model for Fe-pnictides and show
how it affects the spin resonance feature.
|
1608.02230v1
|
2016-08-09
|
Theory Perspective: SCES 2016
|
New discoveries and developments in almost every area of correlated electron
physics were presented at SCES 2016. Here, I provide a personal perspective on
some of these developments, highlighting some new ideas in computational
physics, discussing the "hidden order" challenges of cuprate and heavy electron
superconductors, the mysterious bulk excitations of the topological Kondo
insulator SmB$_{6}$ and new progress in research on quantum spin ice, iron
based superconductors and quantum criticality.
|
1608.02925v3
|
2016-08-15
|
Design and Measurement of Dipole Magnets for CSNS 1.6GeV RCS
|
The Rapid Cycling Synchrotron (RCS) in Chinese Spallation Neutron Source
(CSNS) accelerates proton beam from 80Mev to 1.6GeV at a repetition rate of
25Hz. All dipole magnets of RCS are operated at AC with biased DC. Aiming at
the properties of these dipole magnets, we take some methods to improve
magnetic field quality in the good region and reduce eddy currents in the iron
core . In this paper, we would present the process of the magnet design and
temperature rise calculation. At the same time, the field measurement results
and temperature test of the prototype magnet are also described and discussed.
|
1608.04199v1
|
2016-08-25
|
Two-dimensional Superconductors with Atomic-scale Thicknesses
|
Recent progress in two-dimensional superconductors with atomic-scale
thicknesses is reviewed mainly from the experimental point of view. The
superconducting systems treated here involve a variety of materials and forms:
elemental-metal ultrathin films and atomic layers on semiconductor surfaces;
interfaces and superlattices of heterostructures made of cuprates, perovskite
oxides, and rare-earth metal heavy-fermion compounds; interfaces of
electric-double-layer transistors; graphene and atomic sheets of
transition-metal dichalcogenide; iron selenide and organic conductors on oxide
and metal surfaces, respectively. Unique phenomena arising from the ultimate
two-dimensionality of the system and the physics behind them are discussed.
|
1608.06997v1
|
2016-09-18
|
Lattice dynamics of KNi2Se2
|
We report the first principle calculations of the lattice dynamics of
KNi$_{2}$Se$_2$ together with the Raman scattering study.\ We have observed
three out of four Raman active modes predicted by the factor group analysis.
Calculated phonon frequencies are in good agreement with experimental
findings.\ Contrary to its iron counterpart (K$_x$Fe$_{2-y}$Se$_2$),
K$_{0.95}$Ni$_{1.86}$Se$_2$ does not show vacancy ordering.
|
1609.05547v1
|
2016-10-08
|
Causal-order superposition as an enabler of free will
|
It is often argued that bottom-up causation under a physicalist, reductionist
worldview precludes free will in the libertarian sense. On the one hand, the
paradigm of classical mechanics makes determinism inescapable, while on the
other, the leading models that allow a role for quantum effects are
noncommittal regarding how conscious agents are supposed to translate
indeterminacy into self-formed choice. Recent developments, however, not only
imply that self-formed decisions are possible, but actually suggest how they
might come about. The cornerstone appears to be causality superposition rather
than quantum-state entanglement, as is usually assumed, and the natural arena
for applying these developments is (perhaps ironically) a framework that was
built without any consideration for quantum effects.
|
1610.02395v1
|
2016-12-12
|
Classification of exoplanets according to density
|
Considering probability distribution as a function of the average density
$\bar{\rho}$ computed for 424 extrasolar planets we identify three log-normal
Gaussian population components. The two most populous components at
$\bar{\rho}\simeq0.7$ g/cc and $\bar{\rho}\simeq7$ g/cc are the ice/gas giants
and iron/rock super-Earths, respectively. A third component at
$\bar{\rho}\simeq30$ g/cc is consistent with brown dwarfs, i.e., electron
degeneracy supported objects. We note presence of several extreme density
planetary objects.
|
1612.03556v1
|
2016-12-21
|
MPS and ACS with an atomic magnetometer
|
We show that a single atomic magnetometer in a magnetically unshielded
environment can be used to perform magnetic particle spectroscopy (MPS) and AC
susceptometry (ACS) on liquid-suspended magnetic nanoparticles. We demonstrate
methods allowing a simultaneous recording of M(H) and dM/dH(H) dependences of
samples containing down to 1 $\mu$g of iron. Our results pave the way towards
an atomic magnetometer based MPI scanner.
|
1612.07094v1
|
2016-12-21
|
Grain boundary relaxation and reconstruction: effect on local magnetic moment
|
We present a detailed numerical study on structure and local magnetic
properties of $\langle 100 \rangle$ symmetric tilt grain boundaries in
bcc-iron. Particular attention is paid to connection between type of grain
boundary relaxation and local magnetic properties. Results from first
principles calculation showed that grain boundary reconstruction leads to
non-uniform distribution of local magnetic moments in grain boundary plane.
This is in contrast with the result obtained in grain boundary plane, where
simple relaxation is observed. Well optimized atomic configurations in the
vicinity of the interface were achieved by simulated annealing optimization
technique improved by combination with genetic algorithm.
|
1612.07181v1
|
2017-01-10
|
The giant effect of magnetic ordering on a sound velocity in a sigma-Fe55Cr45 alloy
|
We studied atomic dynamics of sigma-Fe(100-x)Cr(x) (x=45 and 49.5) alloys
using nuclear inelastic scattering of synchrotron radiation. For the
sigma-Fe55Cr45 alloy, the derived reduced iron-partial density of phonon states
reveal a huge difference in the low-energy region between magnetic and
paramagnetic states. The latter implies a ca.36% increase of the sound velocity
in the magnetic phase, which testifies to a magnetically-induced hardening of
the lattice.
|
1701.02467v1
|
2017-02-01
|
Structural characterization of magnetoferritin
|
The physicochemical characterization of the magnetoferritin biomacromolecule
in terms of morphology, structural and magnetic properties shows that iron
oxides can be efficiently loaded into apoferritin molecules, preserving their
native biocompatible structure and affecting the morphology of the protein
shell.
|
1702.00138v1
|
2017-02-09
|
Site-Selective Antimony Doping in Arsenic Zigzag Chains of 112-type Ca1-xLaxFeAs2
|
Single crystal X-ray diffraction studies were performed for the Sb-doped
112-type iron-based superconductor Ca1-xLaxFeAs2 with the superconducting
transition temperature Tc of 47 K. Doped Sb preferably substituted not for
As(1) in the FeAs layers but for As(2) in the layers of As zigzag chains.
Structural reasons for Tc enhancement by Sb doping were discussed.
|
1702.02672v1
|
2017-02-14
|
Hidden radical reactivity of the [FeO]2+ group of the (hydro)oxide species in the H-abstraction from methane: a DFT and CASPT2 study
|
Reactivity of the [FeO]2+ group in the abstraction of hydrogen from methane
is determined by metastable oxyl state FeIII-O* causing the negative spin
polarization of the methyl moiety as was shown by quantum-chemical means with
the use of model iron hydroxide species FeO(OH)2, Fe2O(OH)5, and Fe4O5(OH)3 as
an example.
|
1702.04092v1
|
2017-04-19
|
Remote Document Encryption - encrypting data for e-passport holders
|
We show how any party can encrypt data for an e-passport holder such that
only with physical possession of the e-passport decryption is possible. The
same is possible for electronic identity cards and driver licenses. We also
indicate possible applications. Dutch passports allow for 160 bit security,
theoretically giving sufficient security beyond the year 2079, exceeding
current good practice of 128 bit security. We also introduce the notion of RDE
Extraction PIN which effectively provides the same security as a regular PIN.
Our results ironically suggest that carrying a passport when traveling abroad
might violate export or import laws on strong cryptography.
|
1704.05647v3
|
2017-05-02
|
Computation of the unifying thread in high temperature superconductors from first principles quantum Monte Carlo
|
It has long been a challenge to describe the origin of unconventional
superconductivity. The two known examples with high Tc, based on iron and
copper, have very different electronic structures, while other materials with
similar electronic structure may not show superconductivity at all. In this
paper, the authors show that by using high accuracy diffusion Monte Carlo
calculations, the unconventional superconductors of both high Tc types form a
cluster at intermediate spin-charge coupling. The spin-charge coupling may
serve as a normal state marker for unconventional superconductivity, and
provides evidence that unconventional superconductivity is due to interaction
of charge with local spins in materials.
|
1705.01008v1
|
2017-06-09
|
Ultrasound attenuation in $s^\pm$-wave two-band superconductors
|
The two-band $s^{\pm}$-wave state is currently considered to be the most
promising candidate for newly discovered iron-based high-$T_c$ superconductors.
In this work we study theoretically the ultrasound attenuation in
$s^{\pm}$-wave two-band superconductors. The impurity effect is calculated
within the $\mathcal{T}$-matrix approximation. In particular, our theory
predict that, when the sizes of two order parameter are comparable, a
Hebel-Slichter peak may show up in the ultrasound attenuation versus
temperature curves. Our calculations also confirmed the presence of the
resonant impurity scattering at low temperature, observed previously by other
authors in the calculation of the NMR relaxation rate $1/T_{1}$.
|
1706.02963v1
|
2017-07-29
|
Thermodynamics of the SmCo5 compound doped with Fe and Ni: an ab initio study
|
SmCo5 permanent magnets exhibit enormous uniaxial magnetocrystalline
anisotropy energy and have a high Curie temperature. However, a low energy
product presents a significant drawback in the performance of SmCo5 permanent
magnets. In order to increase the energy product in SmCo5, we propose
substituting fixed amount of cobalt with iron in a new magnet, SmFe3CoNi, where
inclusion of nickel metal makes this magnet thermodynamically stable. We
further discuss some basic theoretical magnetic properties of the SmCo5
compound.
|
1707.09447v1
|
2017-08-29
|
Prediction of a new efficient permanent magnet SmCoNiFe3
|
We propose a new efficient permanent magnet, SmCoNiFe3, that is a
breakthrough development of the well-known SmCo5 prototype. More modern
neodymium magnets of the Nd-Fe-B type have an advantage over SmCo5 because of
their greater maximum energy products due to their iron-rich stoichiometry. Our
new magnet, however, removes most of this disadvantage of SmCo5 while
preserving its superior high-temperature efficiency over the neodymium magnets.
|
1708.08957v1
|
2017-09-08
|
Enhanced superconducting-fluctuation effects on thermodynamic properties in BCS-BEC-crossover regime
|
Effects of superconducting fluctuation (SCF) on thermodynamic properties of
electron systems in the so-called BCS-BEC-crossover regime are studied. As the
attractive interaction between electrons becomes stronger upon approaching the
BCS-BEC-crossover regime, importance of the mode coupling between SCF
drastically increases. The enhanced mode coupling leads to lowering of both the
zero-field superconducting critical temperature and the depairing field
$B_\text{c2} (T)$. Consequently, SCF-induced contributions to the specific heat
and the diamagnetic susceptibility can seemingly exceed the corresponding
values in the Gaussian approximation. We discuss relevance of the present
results to the anomalous SCF-induced diamagnetic response observed in the iron
selenide (FeSe).
|
1709.02553v1
|
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