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1997-12-06
|
Atmospheric neutrino interactions in Soudan-2
|
A new measurement of the atmospheric numu/nue ratio-of-ratios, 0.61 +- 0.15
+- 0.05, has been obtained using a 3.2-kty exposure of the Soudan-2 underground
detector. This measurement, based upon neutrino reactions in an iron tracking
calorimeter of honeycomb-lattice geometry, is in agreement with the anomalously
low value reported by the underground water detectors.
|
9712281v1
|
1998-08-24
|
Limits on Pauli principle violation by nucleons
|
We consider nuclei produced in core collapse supernovae and subjected to a
high neutron flux. We show that an accelerator mass spectrometry experiment
that searched for traces of anomalous iron isotopes could set limits on the
order of $10^{-20}-10^{-25}$ on (or perhaps discover) Pauli principle violation
by neutrons. A similar search for anomalous Co isotopes could set limits in the
range $10^{-13}-10^{-18}$ on Pauli principle violation by protons. We show that
existing data on Oxygen can be used to set a limit of about $10^{-17}$ in one
proposed model of such violation.
|
9808397v1
|
1999-11-12
|
Muon's Behaviors under Bremsstrahlung with both the LPM effect and the Ter-Mikaelian effect and Direct Pair Production with the LPM effect
|
Differential and integral cross sections of the muon are calculated in the
materials: water, standard rock, iron and lead with and without the LPM effect.
The corresponding cross sections are also calculated with dielectric supression
effect (Ter-Mikaelian effect), in addition to the LPM effect. To demonstrate
the importance of the LPM effect in the bremsstrahlung process, depth intensity
relation of muon, energy spectrum, range distribution and survival probability
are calculated taking into account bremsstrahlung spectrum.
|
9911330v1
|
2000-09-13
|
Nuclear effects and higher twists in F3 structure function
|
We analyze the CCFR collaboration iron target data on the xF3 structure
function making particular emphasis on the extraction of the higher twist
contributions from data. Corrections for nuclear effects are applied in order
to extract data on the structure function of the isoscalar nucleon. Our
analysis confirms the observation made earlier, that the higher twist terms
depend strongly on the level to which QCD perturbation theory analysis is
applied. We discuss the impact of nuclear effects on the higher twist term as
well as on the QCD scale parameter Lambda_{\bar{MS}} extracted from the fit to
data.
|
0009150v1
|
2000-12-06
|
Can We Observe the Quark Gluon Plasma in Cosmic Ray Showers ?
|
The possibility of detection of some features of high energy particle
interactions with detectors placed at medium depths underground through studies
on high energy muons is investigated. These muons carry information about the
early interactions occurring during the development of the hadron cascade near
the top of the atmosphere. They might reveal the effects resulting from
creation of quark gluon plasma in interactions of ultra high energy cosmic ray
iron nuclei with air nuclei.
|
0012068v3
|
2001-12-14
|
Differential Distributions for NLO Analyses of Charged Current Neutrino-Production of Charm
|
Experimental analyses of charged current deep inelastic charm production --
as observed through dimuon events in neutrino-iron scattering -- measure the
strangeness component of the nucleon sea. A complete analysis requires a Monte
Carlo simulation to account for experimental detector acceptance effects;
therefore, a fully differential theoretical calculation is necessary to provide
complete kinematic information. We investigate the theoretical issues involved
in calculating these differential distributions at Next-Leading-Order (NLO).
Numerical results are presented for typical fixed target kinematics. We present
a corresponding FORTRAN code suitable for experimental NLO analysis.
|
0112191v1
|
2003-09-09
|
Re/Os constraint on the time-variability of the fine-structure constant
|
We argue that the accuracy by which the isochron parameters of the decay
$^{187}{\rm Re}\to ^{187}{\rm Os}$ are determined by dating iron meteorites may
not directly constrain the possible time-dependence of the decay rate and hence
of the fine-structure constant $\alpha$. From this point of view, some of the
attempts to analyze the Oklo constraint and the results of the QSO absorption
lines are re-examined.
|
0309087v2
|
2003-10-01
|
NUFACT'03: The Fate of the Clones
|
We present a Neutrino-Factory-based setup with three detectors of different
kind in principle capable to solve the eightfold-degeneracy in the simultaneous
measurement of $\theta_{13}$ and $\delta$, for $\theta_{13} \geq 1^\circ
(\sin^2 (2 \theta_{13}) \geq 10^{-3})$. Our setup includes a Superbeam-driven
water Cherenkov (the Superbeam conceived as the first stage of the Neutrino
Factory); two muon-storage-ring-driven detectors (namely, a large magnetized
iron calorimeter and an emulsion cloud chamber) to take advantage of both the
so-called "golden" ($\nu_e \to \nu_\mu$) and "silver" ($\nu_e \to \nu_\tau$)
channels.
|
0310014v1
|
2004-08-23
|
Possible Explanations for the NuTeV Weinberg Angle Measurement
|
The NuTeV collaboration has made an independent determination of the Weinberg
angle by measuring charged and neutral-current cross sections from neutrino and
antineutrino DIS on iron. Their value differs by 3 standard deviations from
that obtained from measurements at the Z pole. We review this experiment and
assess various possible explanations for this result, both within the Standard
Model ("old physics") and outside the Standard Model ("new physics").
|
0408243v2
|
2005-09-22
|
Moments of nuclear and nucleon structure functions at low Q^2 and the momentum sum rule
|
New nuclear structure function data from Jefferson Lab covering the higher x
and lower Q^2 regime make it possible to extract the higher order F_2 moments
for iron and deuterium at low four-momentum transfer squared Q^2. These moments
allow for an experimental investigation of the nuclear momentum sum rule and a
direct comparison of the non-singlet nucleon moment with Lattice QCD results.
|
0509241v2
|
2005-12-09
|
New solutions for the color-flavor locked strangelets
|
Recent publications rule out the negatively charged beta equilibrium
strangelets in ordinary phase, and the color-flavor locked (CFL) strangelets
are reported to be also positively charged. This letter presents new solutions
to the system equations where CFL strangelets are slightly negatively charged.
If the ratio of the square-root bag constant to the gap parameter is smaller
than 170 MeV, the CFL strangelets are more stable than iron and the normal
unpaired strangelets. For the same parameters, however, the positively charged
CFL strangelets are more stable.
|
0512112v1
|
2006-10-04
|
Can we learn something more on oscillations from atmospheric neutrinos?
|
We show that for long-baseline experiments using a Mt water Cerenkov detector
atmospheric neutrino data provide a powerful method to resolve parameter
degeneracies. In particular, the combination of long-baseline and atmospheric
data increases significantly the sensitivity to the neutrino mass hierarchy and
the octant of $\theta_{23}$. Furthermore, we discuss the possibility to use
$\mu$-like atmospheric neutrino data from a big magnetized iron calorimeter to
determine the neutrino mass hierarchy.
|
0610053v1
|
1999-12-23
|
On the discovery of doubly-magic $^{48}$Ni
|
The paper reports on the first observation of doubly-magic Nickel-48 in an
experimental at the SISSI/LISE3 facility of GANIL. Four Nickel-48 isotopes were
identified. In addition, roughly 100 Nickel-49, 50 Iron-45, and 290 Chromium-42
isotopes were observed. This opens the possibility to search for two-proton
emission from these nuclei.
|
9912012v1
|
2006-09-06
|
Dynamics Of Hadronization From Nuclear Semi Inclusive Deep Inelastic Scattering
|
The CLAS experiment E02-104, part of the EG2 run at Jefferson Lab, was
performed to study the hadronization process using semi inclusive deep
inelastic scattering off nuclei. Electron beam energy of 5 GeV and the CLAS
large acceptance detector were used to study charged pion production. The high
luminosity available at Jefferson Lab and the CLAS large acceptance are key
factors for such measurements allowing high statistics and therefore
multidimensional analyses of the data. Both the multiplicity ratio and the
transverse momentum broadening for carbon, iron and lead relative to deuterium
are measured. Preliminary results for positive pions are discussed.
|
0609005v1
|
1997-03-17
|
Fermionic Molecular Dynamics: Multifragmentation in heavy-ion collisions and in excited nuclei
|
Within Fermionic Molecular Dynamics we investigate fragmentation of a
compound system which was created in a heavy-ion collision at a beam energy in
the Fermi energy domain and the decay of excited iron nuclei. We show that in
FMD many-body correlations play an important role in the formation of
fragments.
|
9703035v1
|
1997-07-17
|
Total and Parity-Projected Level Densities of Iron-Region Nuclei in the Auxiliary Fields Monte Carlo Shell Model
|
We use the auxiliary-fields Monte Carlo method for the shell model in the
complete $(pf+0g_{9/2})$-shell to calculate level densities. We introduce
parity projection techniques which enable us to calculate the parity dependence
of the level density. Results are presented for $^{56}$Fe, where the calculated
total level density is found to be in remarkable agreement with the
experimental level density. The parity-projected densities are well described
by a backshifted Bethe formula, but with significant dependence of the
single-particle level-density and backshift parameters on parity. We compare
our exact results with those of the thermal Hartree-Fock approximation.
|
9707027v1
|
2000-09-05
|
Signature of a Pairing Transition in the Heat Capacity of Finite Nuclei
|
The heat capacity of iron isotopes is calculated within the interacting shell
model using the complete $(pf+0g_{9/2})$-shell. We identify a signature of the
pairing transition in the heat capacity that is correlated with the suppression
of the number of spin-zero neutron pairs as the temperature increases. Our
results are obtained by a novel method that significantly reduces the
statistical errors in the heat capacity calculated by the shell model Monte
Carlo approach. The Monte Carlo results are compared with finite-temperature
Fermi gas and BCS calculations.
|
0009006v1
|
2000-12-08
|
Effect of nuclear structure on Type Ia supernova nucleosynthesis
|
The relationship among nuclear structure, the weak processes in nuclei, and
astrophysics becomes quite apparent in supernova explosion and nucleosynthesis
studies. In this brief article, I report on progress made in the last few years
on calculating electron capture and beta-decay rates in iron-group nuclei. I
also report on applications of these rates to Type-Ia nucleosynthesis studies.
|
0012027v1
|
2002-01-10
|
Neutral-current neutrino reactions in the supernova environment
|
We study the neutral-current neutrino scattering for four nuclei in the iron
region. We evaluate the cross sections for the relevant temperatures during the
supernova core collapse and derive Gamow-Teller distributions from large-scale
shell-model calculations. We show that the thermal population of the excited
states significantly enhances the cross sections at low neutrino energies.
Calculations of the outgoing neutrino spectra indicate the prospect of neutrino
upscattering at finite temperatures. Both results are particularly notable in
even-even nuclei.
|
0201025v1
|
2003-03-06
|
Gamow-Teller strength distributions in Fe and Ni stable isotopes
|
We study Gamow-Teller strength distributions in some selected nuclei of
particular Astrophysical interest within the iron mass region. The theoretical
framework is based on a proton-neutron Quasiparticle Random Phase Approximation
built on a deformed selfconsistent mean field basis obtained from two-body
density-dependent Skyrme forces. We compare our results to available
experimental information obtained from (n,p) and (p,n) charge exchange
reactions.
|
0303015v1
|
2006-07-27
|
Spin projection in the shell model Monte Carlo method and the spin distribution of nuclear level densities
|
We introduce spin projection methods in the shell model Monte Carlo approach
and apply them to calculate the spin distribution of level densities for
iron-region nuclei using the complete $(pf+g_{9/2})$-shell. We compare the
calculated distributions with the spin-cutoff model and extract an
energy-dependent moment of inertia. For even-even nuclei and at low excitation
energies, we observe a significant suppression of the moment of inertia and
odd-even staggering in the spin dependence of level densities.
|
0607062v1
|
2000-03-22
|
RF-induced evaporative cooling and BEC in a high magnetic field
|
We present the design of our iron-core electromagnet for BEC, and how to
solve the specific experimental problems raised by this technique. After
presenting the experimental set-up, we address the interruption of runaway
evaporative cooling when the Zeeman effect is not linear. We present the ways
to circumvent this problem, use of multiple RF frequencies, sympathetic cooling
and show some applications of these high magnetic fields (cavity coupling, high
confinement).
|
0003050v1
|
2007-02-13
|
LHCb Level-0 Trigger Detectors
|
The calorimeter and muon systems are essential components to provide a
trigger for the LHCb experiment. The calorimeter system comprises a
scintillating pad detector and pre-shower, followed by electromagnetic and
hadronic calorimeters. The calorimeter system allows photons, electrons and
hadrons to be identified, and their energy to be measured. The muon system
consists of five measuring stations equipped with Multi-Wire Proportional
Chambers (MWPCs) and triple-Gas Electron Multiplier (GEM) detectors, separated
by iron filters. It allows the muons identification and transverse momentum
measurement. The status of the two systems and their expected performance is
presented.
|
0702103v1
|
2006-03-21
|
Quantum description of spin tunneling in magnetic molecules: a new view
|
Starting from a phenomenological Hamiltonian originally written in terms of
angular momentum operators we derive a new quantum angle-based Hamiltonian that
allows for a discussion on the quantum spin tunneling. The study of the
applicability of the present approach, carried out in calculations with a
soluble quasi-spin model, shows that we are allowed to use our method in the
description of physical systems such as the Mn12-acetate molecule, as well as
the octanuclear iron cluster, Fe8, in a reliable way. With the present
description the interpretation of the spin tunneling is seen to be direct, the
spectra and energy barriers of those systems are obtained, and it is shown that
they agree with the experimental ones.
|
0603183v1
|
2007-02-06
|
Spin tunneling in magnetic molecules: Quantitative estimates for Fe8 clusters
|
Spin tunneling in the particular case of the magnetic molecular cluster
octanuclear iron(III), Fe8, is treated by an effective Hamiltonian that allows
for an angle-based description of the process. The presence of an external
magnetic field along the easy axis is also taken into account in this
description. Analytic expressions for the energy levels and barriers are
obtained from a harmonic approximation of the potential function which give
results in good agreement with the experimental results. The energy splittings
due to spin tunneling is treated in an adapted WKB approach and it is shown
that the present description can give results to a reliable degree of accuracy.
|
0702051v1
|
2007-04-19
|
Iron Line Profiles from Relativistic Thick Accretion Disk
|
We present a new code for calculating the Fe Kalpha line profiles from
relativistic accretion disks with finite thickness around a rotating black
hole. The thin Keplerian accretion disk must become thicker and sub-Keplerian
with increasing accretion rates. We here embark on, for the first time, a fully
relativistic computation which is aimed at gaining an insight into the effects
of geometrical thickness and the sub-Keplerian orbital velocity on the line
profiles. This code is also well-suited to produce accretion disk images.
|
0704.2460v1
|
2007-04-20
|
Neutrino beams as a probe of the nuclear isospin and spin-isospin excitations
|
We explore the possibility of performing nuclear structure studies using low
energy neutrino beams. In particular, low energy beta-beams and conventional
sources (muon decay-at-rest) are considered. We present results on the total
charged-current as well as flux-averaged cross sections associated to electron
(anti)-neutrino scattering on oxygen, iron, molybdenum and lead, as typical
examples. It is shown that by using neutrinos from low energy beta-beams,
information on forbidden states, in particular the spin-dipole, could be
extracted.
|
0704.2724v2
|
2007-05-14
|
On the Enhanced Reverse Beta Processes in Graphene-Iron Composite Nanostructures at High Temperatures in Strong Magnetic Field
|
Strong dense many-spin interactions have been proposed to organize novel
orbital dynamics (the Little Effect) for novel chemical and catalytic
phenomena. The recent determinations of the relativistic and quantum Hall
effects of carriers in graphene under strong magnetic confinement have
substantiated the Little Effect. Moreover such nonclassical phenomena under the
stronger magnetic confinement of ferro-nanocatalysts are here shown to organize
reverse beta processes and possibly pycnonuclear reactions under high
temperature and high-pressure conditions. Such processes have implications for
reverse beta reactions and nuclear reactions within the interior of the earth
and new technologies for carbon nanotube-ferrometal and nanographene-ferrometal
composites.
|
0705.1909v1
|
2007-06-22
|
A cool R Coronae Borealis star Z UMi
|
The high resolution spectra of a R CrB type star Z UMi are analysed. The
atmospheric parameters of Z UMi are estimated: Teff=5250+/-250K and log
g=0.5+/-0.3. This places Z UMi among the coolest R CrB stars. The hydrogen
deficiency of Z UMi is confirmed. The abundances of other elements resemble
those found for the minority group of R CrB stars. We note very low iron
abundance, [Fe/H]=-1.85, and an excess of lithium, [Li/Fe]=+1.9.
|
0706.3271v1
|
2007-06-27
|
Molecular dynamics simulations of the dipolar-induced formation of magnetic nanochains and nanorings
|
Iron, cobalt and nickel nanoparticles, grown in the gas phase, are known to
arrange in chains and bracelet-like rings due to the long-range dipolar
interaction between the ferromagnetic (or super-paramagnetic) particles. We
investigate the dynamics and thermodynamics of such magnetic dipolar
nanoparticles for low densities using molecular dynamics simulations and
analyze the influence of temperature and external magnetic fields on two- and
three-dimensional systems. The obtained phase diagrams can be understood by
using simple energetic arguments.
|
0706.3920v1
|
2007-07-23
|
Magic Baseline Beta Beam
|
We study the physics reach of an experiment where neutrinos produced in a
beta-beam facility at CERN are observed in a large magnetized iron calorimeter
(ICAL) at the India-based Neutrino Observatory (INO). The CERN-INO distance is
close to the so-called "magic" baseline which helps evade some of the parameter
degeneracies and allows for a better measurement of the neutrino mass hierarchy
and $\theta_{13}$.
|
0707.3367v1
|
2007-08-09
|
The Rest-Frame UV Spectrum of Elliptical Galaxies at High Redshift
|
Beyond redshift ~1.4 the only spectral feature that allows one to get the
redshift of passively evolving galaxies (PEG) with optical spectrographs is a
characteristic structure due to a set of iron and magnesium lines lines at
2600-2850 Angstrom in the rest frame. The same feature permits also to estimate
the time elapsed since the cessation of star formation. Current efforts at
observing high redshift PEGs at the VLT and SUBARU telescopes are briefly
reviewed.
|
0708.1240v1
|
2007-09-03
|
Galactic neutrino background from cosmic ray interaction with the ISM content
|
We use a diffusive model for the propagation of Galactic cosmic rays to
estimate the charged pion production in interactions with protons of the
interstellar medium. Cosmic ray nuclei from proton to iron are considered and
the corresponding contribution to the neutrino secondary flux produced as a
result of spallation is also estimated.
|
0709.0278v2
|
2007-09-06
|
Structural peculiarities of plastically-deformed cementite and their influence on magnetic characteristics and Mossbauer parameters
|
Cementite Fe3C is studied with first-principles calculations. Two possible
positions of carbon atoms in the iron sublattice are considered: with prismatic
or octahedral environment. Mossbauer spectra (MS) with parameters calculated
for both modifications are simulated above and below the Curie temperature. A
possibility to detect the change in carbon position upon annealing from MS is
discussed. It is shown that this is hardly possible using a standard approach
to treatment of MS, but it can be seen in more subtle details of the MS below
the Curie temperature, such as widths and positions of separate lines.
|
0709.0789v1
|
2007-11-28
|
Nuclear effects in F_3 structure function of nucleon
|
We study nuclear effects in the $F^A_3(x)$ structure function in the deep
inelastic neutrino reactions on iron by using a relativistic framework to
describe the nucleon spectral functions in the nucleus.
The results for the ratio $R(x,Q^2)=\frac{F^A_3(x,Q^2)}{AF^N_3(x, Q^2)}$ and
the Gross-Llewellyn Smith(GLS) integral $G(x,Q^2)=\int_x^1 dx F^A_3(x,Q^2)$ in
nuclei are discussed and compared with the recent results available in
literature from theoretical and phenomenological analyses of experimental data.
|
0711.4443v2
|
2007-12-05
|
Investigating Possible Neutrino Decay in Long Baseline Experiment Using ICAL as Far end Detector
|
We investigate the effects of possible decay of neutrinos from a neutrino
factory in a long baseline experiment. We consider the neutrinos from a factory
at CERN and the detector to be the 50 kTon iron calorimeter (ICAL) detector
proposed for India-based Neutrino Observatory (INO). We found considerable
depletion of muon yield at INO for certain value of decay parameters.
|
0712.0697v2
|
2007-12-20
|
On the Simbol-X capability of detecting red/blue-shifted emission and absorption Fe K lines
|
The detection of red/blue-shifted iron lines in the spectra of astronomical
X-ray sources is of great importance, as it allows to trace the environment
around compact objects, like black holes in AGNs. We report on extensive
simulations to test the Simbol-X capability of detecting such spectral
features, focusing on the low energy detector (0.5-30 keV).
|
0712.3427v1
|
2008-01-16
|
Light-induced scattering and energy transfer between orthogonally-polarized waves
|
We present a detailed experimental investigation on polarization-isotropic
and polarization-anisotropic holographic scattering in lithium niobate crystal
doped with iron when recording parasitic gratings with an ordinary polarized
pump beam. The kinetics of both types of scattering during the whole process of
recording is studied. Holographic scattering is presented as a simple technique
to monitor the energy transfer between beams of different polarization.
Moreover, the spectral and the angular dependence of the transmitted intensity
of the crystal during the reconstruction of the auto-generated parasitic
gratings are measured.
|
0801.2489v1
|
2008-01-30
|
Long-range magnetic order and spin-lattice coupling in the delafossite CuFeO2
|
The electronic and magnetic properties of the delafossite CuFeO2 are
investigated by means of electronic structure calculations. They are performed
using density functional theory in the generalized gradient approximation as
well as the new full-potential augmented spherical wave method. The
calculations reveal three different spin states at the iron sites. Taking into
account the correct crystal structure, we find long-range antiferromagnetic
ordering in agreement with experiment. Contrasting previous work, our
calculations show that non-local exchange interactions lead to a semiconducting
ground state.
|
0801.4787v1
|
2008-01-31
|
The Impact of Transit Observations on Planetary Physics
|
We highlight the importance of transit observations on understanding the
physics of planetary atmospheres and interiors. Transmission spectra and
emission spectra allow us to characterize this exotic atmospheres, which
possess TiO, VO, H2O, CO, Na, and K, as principal absorbers. We calculate
mass-radius relations for water-rock-iron and gas giant planets and examine
these relations in light of current and future transit observations. A brief
review is given of mechanisms that could lead to the large radii observed for
some transiting planets.
|
0801.4943v1
|
2008-02-06
|
The Suppression and Recovery of the Ferroelectric Phase in Multiferroic $MnWO_4$
|
We report the discovery of a complete suppression of ferroelectricity in
$MnWO_4$ by 10 % iron substitution and its restoration in external magnetic
fields. The spontaneous polarization in $Mn_{0.9}Fe_{0.1}WO_4$ arises below 12
K in external fields above 4 T. The magnetic/ferroelectric phase diagram is
constructed from the anomalies of the dielectric constant, polarization,
magnetization, and heat capacity. The observations are qualitatively described
by a mean field model with competing interactions and strong anisotropy. We
propose that the magnetic field induces a non-collinear inversion symmetry
breaking magnetic structure in $Mn_{0.9}Fe_{0.1}WO_4$.
|
0802.0839v1
|
2008-03-31
|
Hole superconductivity in Arsenic-Iron compounds
|
Superconductivity above 25K, and possibly above 40K, has recently been
discovered in $LaO_{1-x}F_xFeAs$ and related compounds. We propose that this is
another example of the mechanism of hole superconductivity at play. This
requires the existence of hole carriers at the Fermi energy, which appears to
contradict current observations. We propose that two-band conduction is taking
place in these materials, that the negative ion $As^{-3}$ plays a key role, and
that superconductivity is non-phononic and driven by pairing and undressing of
heavily dressed hole carriers to lower their kinetic energy. We make several
predictions of future observations based on our theory.
|
0804.0002v1
|
2008-04-03
|
Understanding the Unique Structural and Electronic Properties of SrFeO2
|
We report a first-principles study of SrFeO$_2$, an infinite-layer oxide with
Fe atoms in a perfect square-planar coordination down to essentially 0 K. Our
results reveal this striking behavior relies on the double occupation of the
3$d_{z^2}$ orbitals of high-spin Fe$^{2+}$. Such an electronic state results
from the hybridization of iron's 3$d_{z^2}$ and 4$s$ orbitals, which enables a
large reduction of the intra-atomic exchange splitting of the $z^2$ electrons.
The generality of the phenomenon is discussed.
|
0804.0495v1
|
2008-04-21
|
Unusual magnetic behavior in ferrite hollow nanospheres
|
We report unusual magnetic behavior in iron oxide hollow nanospheres of 9.3
$nm$ in diameter. The large fraction of atoms existing at the inner and outer
surfaces gives rise to a high magnetic disorder. The overall magnetic behavior
can be explained considering the coexistence of a soft superparamagnetic phase
and a hard phase corresponding to the highly frustrated cluster-glass like
phase at the surface regions.
|
0804.3292v1
|
2008-04-24
|
Graphene-protected iron layer on Ni(111)
|
Here we report the photoemission studies of intercalation process of Fe
underneath graphene layer on Ni(111). The process of intercalation was
monitored via XPS of corresponding core levels and UPS of the graphene-derived
$\pi$ states in the valence band. \textit{fcc}-Fe films with thickness of 2-5
monolayers at the interface between graphene and Ni(111) form epitaxial
magnetic layer passivated from the reactive environment, like for example
oxygen gas.
|
0804.3942v1
|
2008-04-24
|
19-F NMR Investigation of Iron-pnictide Superconductor LaFeAsO(0.89)F(0.11)
|
We report 19-F NMR investigation of the new high temperature superconductor
LaFeAsO(0.89)F(0.11) (Tc ~ 28K). We demonstrate that low frequency spin
fluctuations exhibit pseudo gap behavior above Tc. We also deduce the London
penetration depth lambda from NMR line broadening below Tc.
|
0804.4026v3
|
2008-04-25
|
Structural, magnetic and electronic properties of quaternary oxybismuthides LaOMBi (where M = Sc, Ti ... Ni, Cu) - possible parent phases for new superconducting materials
|
The extensive ab initio total energy calculations using the VASP-PAW method
with the generalized gradient approximation (GGA) for the exchange-correlation
potential are applied to systematic investigation of structural, electronic and
magnetic properties in quaternary oxybismuthides LaOMBi (where M = Sc, Ti...Ni,
Cu). The energy spectrum features similar to lanthanum-iron oxyarsenide LaOFeAs
and non-magnetic ground state are indicative of superconductivity possible in
lanthanum-nickel oxybismuthide LaONiBi.
|
0804.4064v1
|
2008-05-23
|
Normal State Correlated Electronic Structure of Iron Pnictides
|
We describe the correlated electronic structure of a prototype Fe-pnictide
superconductor, $SmO_{1-x}F_{x}FeAs$, using LDA+DMFT. Strong, multi-orbital
electronic correlations generate a low-energy pseudogap in the undistorted
phase, giving a bad, incoherent metal in qualitative agreement with
observations. Very good semi-quantitative agreement with the experimental
spectral functions is seen, and interpreted, within a correlated, multi-orbital
picture. Our results show that Fe-pnictides should be understood as low-carrier
density, incoherent metals, in resemblance to the underdoped cuprate
superconductors.
|
0805.3636v1
|
2008-05-26
|
Observation of magnetic field lines in the vicinity of a superconductor with the naked eye
|
Meissner effect and pinning effect are clearly observed with the naked eye. A
GdBaCuO high-temperature superconductor (HTS) disk fabricated by Nippon Steel
Corporation, a 100mm cubic NdFeB sintered magnet, and iron wires coated by
colored are used. When the HTS is put in the magnetic field of the magnet, it
can be observed by the wires that the magnetic field lines are excluded from
the superconductor (Meissner effect) as well as are pinned in the
superconductor (pinning effect).
|
0805.3990v4
|
2008-06-05
|
Low temperature synthesis and pressure induced insulator-metal transition of the newly found NdFeAsO0.75
|
As low as 900 oC, iron-based layered quaternary compound NdFeAsO0.75 was
synthesized through solid state reaction method. XRD measurements illustrate
almost pure phase of tetragonal phase NdFeAsO was formed. The synthesis
temperature in our experiment is the lowest among all the reported methods
without the help of any mineralizer. After further treatment under high
pressure of 6 GPa at temperature of 1300 oC for 2 hours, the electrical
transport property of NdFeAsO0.75 was transformed from insulator-like to metal-
like behavior.
|
0806.0976v1
|
2008-06-11
|
On superconducting and magnetic properties of iron-oxypnictides
|
Pairing symmetry in oxypnictides, a new family of multiband high-Tc
superconductors, is partially imposed by the positions of multiple Fermi
pockets, which itself can give rise to new order parameters, such as s+,-
states or the state of dx^2-y^2 symmetry. Other pairing states may appear on
small pockets for long range interactions, but they are expected to be
sensitive to defects. We identify the competing antiferromagnetic order with
the triplet exciton transition in the semi- metallic background and discuss
whether its coexistence with superconductivity explains the doping dependence
of Tc.
|
0806.1933v2
|
2008-06-14
|
Pressure-induced superconductivity in PrOxFeAs
|
Superconductivity with Tc of 45 K was realized in the tetragonal
ZrCuSiAs-type PrOxFeAs (x=0.75) under heat treatment of 1300 oC and pressure of
6 GPa for 2 hours. Although the sample prepared at 900 oC in vaccum possessed
the same phase as that treated in pressure, the electrical transport
measurement showed the similar behavior with its parent ReOFeAs (Re: rare-earth
metal). This pressure-induced superconductivity could give us a hint to
understand the origins of the newly-found iron based superconductors.
|
0806.2379v1
|
2008-06-17
|
Improved parameters of the hydrogen-deficient binary star KSPer
|
Using the high resolution spectral observations obtained with the Nasmyth
Echelle Spectrograph NES of the 6m telescope we analysed the optical spectrum
of the hydrogen-deficient binary star KSPer. The atmospheric parameters derived
are: effective temperature Teff=9500+/-300 K, surface gravity log g=2.0+/-0.5,
and microturbulent velocity Vt=9.5+/-0.5km/s. The hydrogen deficiency is
H/He=3x10^{-5}, iron abundance is reduced by 0.8dex; nitrogen abundance is very
high [N/Fe]=1.4, but carbon and oxygen abundances are low. The star luminosity
is log L/Lo=3.3. A complex absorption and emission structure of the NaI D
doublet was revealed. We suggest that the emission component forms in the
circumbinary gaseous envelope.
|
0806.2709v1
|
2008-06-19
|
Real Space Coulomb Interaction: A Pairing Glue for FeAs Superconductors
|
In this paper we present a real space pairing glue for the iron-based layered
superconductors. It is shown that two static electrons embedded symmetrically
into two adjacent Fe plaquettes of the superconductor can be bounded due to the
Coulombic interaction. The pairing mechanism favors the existence of the
pseudogap in the underdoped FeAs superconductors. A criterion is introduced to
distinguish whether or not the pseudogap can open in a material.
|
0806.3125v2
|
2008-06-25
|
Mossbauer Spectroscopy Determination of iron foreign phases in the Superconducting Systems; RAsFeO1-x, RAsFeO1-xFx and Sr1-xKxFe2As2
|
The recently discovered superconducting - spin density wave materials,
containing Fe and As, have raised huge interest. However most materials
prepared to date, suffer from a varying degree of content of foreign Fe-As
phases, Fe2As, FeAs2 and FeAs, which can lead to wrong conclusions concerning
the properties of these materials. We show here that Mossbauer Spectroscopy is
able to determine quite easily the relative content of the foreign phases. This
procedure is demonstrated by a study of seven samples of superconducting or
spin density wave materials, prepared in three different laboratories.
|
0806.4078v1
|
2008-06-26
|
Some improvements of the ART method for finding transition pathways on potential energy surfaces
|
The Activation-Relaxation Technique nouveau (ARTn) is an eigenvector
following method for systematic search of saddle points and transition pathways
on a given potential energy surface. We propose a variation of this method
aiming at improving the efficiency of the local convergence close to the saddle
point. We prove the convergence and robustness of this new algorithm. The
efficiency of the method is tested in the case of point defects in body
centered cubic iron.
|
0806.4354v1
|
2008-07-14
|
Superconductivity in SrFe_(2-x)Co_xAs_2: Internal Doping of the Iron Arsenide Layers
|
In the electron doped compounds SrFe_(2-x)Co_xAs_2 superconductivity with T_c
up to 20 K is observed for 0.2 < x < 0.4. Results of structure determination,
magnetic susceptibility, electrical resistivity, and specific heat are
reported. The observation of bulk superconductivity in all thermodynamic
properties -- despite strong disorder in the Fe-As layer -- favors an itinerant
picture in contrast to the cuprates and renders a p- or d-wave scenario
unlikely. DFT calculations find that the substitution of Fe by Co (x > 0.3)
leads to the suppression of the magnetic ordering present in SrFe_2As_2 due to
a rigid down-shift of the Fe-3d_(x^2-y^2) related band edge in the density of
states.
|
0807.2223v1
|
2008-07-14
|
Structure and superconductivity of LiFeAs
|
The lithium ions in Lithium iron arsenide phases with compositions close to
LiFeAs have been located using powder neutron diffraction. These phases exhibit
superconductivity at temperatures at least as high as 16 K demonstrating that
superconductivity in compounds with [FeAs]- anti-PbO-type anionic layers occurs
in compounds with at least three different structure types and occurs for a
wide range of As-Fe-As bond angles.
|
0807.2228v2
|
2008-07-31
|
Superconductivity in nickel-based compound GdONiBi and hole doped Gd0.9Sr0.1ONiBi
|
We successfully synthesized the nickel-based compound GdONiBi with
superconducting transition temperature about 4.5 K. By partially substituting
the element Gd with Sr to introduce holes into the material, we got new
superconductor Gd0.9Sr0.1ONiBi with critical temperature about 4.7 K. The
normal state resistivity in nickel-based samples shows a metallic behavior. The
magnetoresistance measurements show a different behavior compared to those in
iron-based compounds which indicates that the mechanism in the two kinds of
superconductors maybe different.
|
0807.5045v1
|
2008-08-04
|
Superconductivity in Co-doped SmFeAsO
|
Here we report the synthesis and basic characterization of SmFe1-xCoxAsO
(x=0.10, 0.15). The parent compound SmFeAsO itself is not superconducting but
shows an antiferromagnetic order near 150 K, which must be suppressed by doping
before superconductivity emerges. With Co-doping in the FeAs planes,
antiferromagnetic order is destroyed and superconductivity occurs at 15 K.
Similar to LaFe1-xCoxAsO, the SmFe1-xCoxAsO system appears to tolerate
considerable disorder in the FeAs planes. This result is important, which
indicates difference between cuprare superconductors and the iron-based
arsenide ones.
|
0808.0197v2
|
2008-08-13
|
Superconductivity in layered iron Selenide induced by cobalt- and sodium-doping
|
Superconductivity with zero resistance transition temperature (Tc) up to 8.4
K and 8.3 K can be obtained by doping cobalt and sodium in alfa-FeSe with the
nominal composition of Fe0.92Co0.08Se and Na0.1FeSe, respectively. The
electrical resistivity and AC magnetic susceptibility of the prepared samples,
measured with physical property measurement system (PPMS), unambiguously
consistent with each other to indicate that the samples are superconductive.
The respective doping mechanisms for cobalt and sodium into the parent
alfa-FeSe are the Fe-site substitution and the interlayer insertion. It is the
first time that alfa-FeSe can be induced to be a superconductor with Na+
intercalated into the interlayers.
|
0808.1784v1
|
2008-08-14
|
Heteroepitaxial growth and optoelectronic properties of layered iron oxyarsenide, LaFeAsO
|
Epitaxial thin films of LaFeAsO were fabricated on MgO (001) and
mixed-perovskite (La, Sr)(Al, Ta)O3 (001) single-crystal substrates by pulsed
laser deposition using a Nd:YAG second harmonic source and a 10 at.% F-doped
LaFeAsO disk target. Temperature dependences of the electrical resistivities
showed no superconducting transition in the temperature range of 2-300 K, and
were similar to those of undoped polycrystalline bulk samples. The
transmittance spectrum exhibited a clear peak at ~0.2 eV, which is explained by
ab-initio calculations.
|
0808.1956v2
|
2008-08-28
|
Electric excitation of spin resonance in antiferromagnetic conductors
|
Antiferromagnetism couples electron spin to its orbital motion, thus allowing
excitation of electron-spin transitions by an ac electric rather than magnetic
field - with absorption, exceeding that of common electron spin resonance at
least by four orders of magnitude. In addition to potential applications in
spin electronics, this phenomenon may be used as a spectroscopy to study
antiferromagnetic materials of interest - from chromium to borocarbides,
cuprates, iron pnictides, and organic and heavy fermion conductors.
|
0808.3946v2
|
2008-08-30
|
A new family of iron pnictides: BaFeAs2 and BaFeSb2
|
We investigate the structural, electronic, and magnetic properties of the
hypothetical compound BaFePn2 (Pn = As and Sb), which is isostructural to the
parent compound of the high temperature superconductor LaFeAsO1-xFx. Using
density functional theory, we show that the Fermi surface, electronic structure
and the spin density wave instability of BaFePn2 are very similar to the Fe
based superconductors. Additionally, there are very dispersive metallic bands
of a spacer Pn layer, which are almost decoupled from FePn layer. Our results
show that experimental study of BaFePn2 can test the role of charge and
polarization fluctuation, importance of two dimensionality in mechanism of
superconductivity.
|
0809.0041v2
|
2008-09-03
|
Imaging the antiparallel magnetic alignment of adjacent Fe and MnAs thin films
|
The magnetic coupling between iron and alpha - MnAs in the epitaxial system
Fe/MnAs/GaAs(001) has been studied at the sub-micron scale, using element
selective x-ray photoemission electron microscopy. At room temperature, MnAs
layers display ridges and grooves, alternating alpha (magnetic) and beta
(non-magnetic) phases. The self-organised microstructure of MnAs and the stray
fields that it generates govern the local alignment between the Fe and alpha -
MnAs magnetization directions, which is mostly antiparallel with a marked
dependence upon the magnetic domain size.
|
0809.0620v1
|
2008-09-08
|
Pressure Study of Superconducting Oxypnictide LaFePO
|
Electrical resistivity and magnetic susceptibility measurements under high
pressure were performed on an iron-based superconductor LaFePO. A steep
increase in superconducting transition temperature (Tc) of LaFePO with dTc/dP >
4 K/GPa to a maximum of 8.8 K for P = 0.8 GPa was observed. These results are
similar to isocrystalline LaFeAsO1-xFx system reported previously. X-ray
diffraction measurements were also performed under high pressure up to 10 GPa,
where linear compressibility ka and kc are presented.
|
0809.1239v1
|
2008-09-10
|
Structural and electronic response upon hole-doping of rare-earth iron oxyarsenides Nd1-xSrxFeAsO (0 < x < 0.2)
|
Hole-doping of NdFeAsO via partial replacement of Nd3+ by Sr2+ is a
successful route to obtain superconducting phases (Tc = 13.5 K for a Sr2+
content of 20%); however, the structural and electronic response with doping is
different from and non-symmetric to that in the electron-doped side of the
phase diagram.
|
0809.1755v1
|
2008-09-17
|
Phonon Density of States in Nd(O$_{1-x}$F$_{x}$)FeAs
|
We report measurements of the phonon density-of-states in iron oxypnictide
superconductors by inelastic x-ray scattering. A good agreement with ab-initio
calculations that do not take into account strong electronic correlations is
found, and an unpredicted softening of phonon branches under F doping of these
compounds is observed. Raman scattering experiments lead us to conclude that
this softening is not related to zone center phonons, and consequently imply an
important softening of the relevant phonon branches at finite momentum transfer
Q.
|
0809.2898v1
|
2008-10-08
|
Pressure-induced superconductivity in Iron pnictide compound SrFe2As2
|
Electrical resistivity under high pressure have been measured on nominally
pure SrFe2As2 up to 14 GPa. The resistivity drop appeared with increasing
pressure, and we clearly observed zero resistivity. The maximum of
superconducting transition temperature (Tc) is 38 K. The value is corresponding
to the one of optimally doping AFe2As2 (A=Sr, Ba) system with K+ ions at the
A2+ site.
|
0810.1377v1
|
2008-10-17
|
Magnetic Phase Diagram of FeAs based superconductors
|
The recently discovered high-temperature superconductivity in doped
quaternary iron oxypnictides correlates experimentally with a magnetic
instability. We have used first-principles calculations to determine a magnetic
phase diagram of ReO$_{1-\delta}$FeAs (Re=La--Dy) as a function of the doping
$\delta$, of the FeAs in-plane lattice constant $a$, and of the distance
between the Fe and As planes, that is qualitatively consistent with recent
experimental findings on the doping, internal (chemical) and external pressure
dependence. The existence of a tricritical point (TCP) in the phase diagram
suggests new ways of enhancing $T_c$.
|
0810.3246v1
|
2008-10-18
|
Density Functional Study of Excess Fe in Fe$_{1+x}$Te: Magnetism and Doping
|
The electronic and magnetic properties of the excess Fe in iron telluride
Fe$_{(1+x)}$Te are investigated by density functional calculations. We find
that the excess Fe occurs with valence near Fe$^{+}$, and therefore provides
electron doping with approximately one carrier per Fe, and furthermore that the
excess Fe is strongly magnetic. Thus it will provide local moments that
interact with the plane Fe magnetism, and these are expected to persist in
phases where the magnetism of the planes is destroyed for example by pressure
or doping. These results are discussed in the context of superconductivity.
|
0810.3274v1
|
2008-10-29
|
FeTe as a candidate material for new iron-based superconductor
|
Tetragonal FeSe is a superconductor with a transition temperature Tc of 8 K
and shows a huge enhancement of Tc with applying pressure. Tetragonal FeTe has
a structure very analogous to superconducting FeSe, but does not show
superconducting transition. We investigated the pressure effect of resistivity
on FeTe. The resistivity at room temperature decreased with increasing
pressure. An anomaly in resistivity around 80 K shifted towards a lower
temperature with increasing pressure.
|
0810.5191v1
|
2008-11-08
|
Theory of Magnetic Order in $ Fe_{1+y}Te_{1-x}Se_x$
|
We develop a local spin model to explain the rich magnetic structures in the
iron-based superconductors $Fe_{1+y}Te_{1-x}Se_x$. We show that our model
exhibits both commensurate antiferromagnetic and incommensurate magnetic order
along the crystal a-axis. The transition from the commensurate to the
incommensurate phase is induced when the concentration of excess $Fe$ atoms is
larger than a critical value. Experimentally measurable spin-wave features are
calculated, and the mean-field phase diagram of the model is obtained. Our
model also suggests the existence of a large quantum critical region due to
strong spin frustration upon increasing $Se$ concentration.
|
0811.1294v1
|
2008-11-26
|
Spin-Valve Effect of the Spin Accumulation Resistance in a Double Ferromagnet - Superconductor Junction
|
We have measured the transport properties of Ferromagnet - Superconductor
nanostructures, where two superconducting aluminum (Al) electrodes are
connected through two ferromagnetic iron (Fe) ellipsoids in parallel. We find
that, below the superconducting critical temperature of Al, the resistance
depends on the relative alignment of the ferromagnets' magnetization. This
spin-valve effect is analyzed in terms of spin accumulation in the
superconducting electrode submitted to inverse proximity effect.
|
0811.4252v2
|
2008-11-28
|
Crystalline multilayers of the confined Yukawa system
|
The phase diagram of Yukawa particles confined between two parallel hard
walls is calculated at zero-temperature beyond the bilayer regime by
lattice-sum-minimization. Tuning the screening, a rich phase behavior is found
in the regime bounded by stable two-triangular layers and 3-square layers. In
this regime, alternating prism phases with square and triangular basis,
structures derived from a hcp bulk lattice, and a structure with two outer
layers and two inner staggered rectangular layers, reminiscent of a Belgian
waffle iron, are stable. These structures are verifiable in experiments on
charged colloidal suspensions and dusty plasma sheets.
|
0811.4763v2
|
2008-12-03
|
Relationship between the magnetic hyperfine field and the magnetic moment
|
Based on experimental data it is shown, for some chosen alloys and compounds
of iron, that there is no one unique relationship between the 57Fe-site
magnetic hyperfine field, Bhf, and the magnetic moment per Fe atom, m. Instead,
the Bhf-m plot consists of several branches, each of them being characteristic
of a given alloy or compound. Consequently, the effective proportionality
constant (hyperfine coupling constant) depends on the alloy system or compound,
and for a given alloy system or compound it depends on the composition or even
on the lattice site. Consequently, the scaling of Bhf into the underlying m
cannot be done a priopri.
|
0812.0671v1
|
2008-12-05
|
In-gap bound states and tunneling conductance of multiband superconductors through a normal/superconductor/superconductor junction
|
The tunneling conductance between a metal and a multiband s-wave
superconductor with a thin layer of single-band s-wave superconductor
sandwiched in between is examined in this paper. We show that an in-gap peak in
conductance curve is found as a result of the formation of in-gap bound state
between the single-band and multiband superconductor junctions if the phases of
the superconducting order parameters of the multiband superconductor are
frustrated. The implication of this result in determining the gap symmetry of
the iron-based superconductors is discussed.
|
0812.1068v2
|
2008-12-12
|
Physics Potential of Future Atmospheric Neutrino Searches
|
The potential of future high statistics atmospheric neutrino experiments is
considered, having in mind currently discussed huge detectors of various
technologies (water Cerekov, magnetized iron, liquid Argon). I focus on the
possibility to use atmospheric data to determine the octant of $\theta_{23}$
and the neutrino mass hierarchy. The sensitivity to the $\theta_{23}$-octant of
atmospheric neutrinos is competitive (or even superior) to long-baseline
experiments. I discuss the ideal properties of a fictitious atmospheric
neutrino detector to determine the neutrino mass hierarchy.
|
0812.2392v1
|
2008-12-12
|
Interplay between magnetism and superconductivity in Fe-pnictides
|
We consider phase transitions and potential co-existence of spin-density-wave
(SDW) magnetic order and extended s-wave ($s^+$) superconducting order within a
two-band itinerant model of iron pnictides, in which SDW magnetism and $s^+$
superconductivity are competing orders. We show that depending on parameters,
the transition between these two states is either first order, or involves an
intermediate phase in which the two orders co-exist. We demonstrate that such
co-existence is possible when SDW order is incommensurate.
|
0812.2469v1
|
2008-12-22
|
The calculation of the effective interaction parameter in LDA+U method by linear response approach for Fe(OH)2
|
In this paper we have investigated the electronic properties of Fe(OH)2
hydroxide by using the LSDA+U as well as the generalized gradient
approximation. Our calculations for the iron-hydroxide show that the LSDA
results are greatly at variance with experimental findings. On the other hand
we have shown that LSDA+U is capable of opening a gap at the Fermi level
resulting in insulating ground state in agreement with experimental
observations.
|
0812.4116v1
|
2008-12-30
|
Maxwell Tension Supports the Water Bridge
|
A cylindrical flexible cable made up of pure fluid water can be
experimentally spanned across a spatial gap with cable endpoints fixed to the
top edges of two glass beakers. The cable has been called a water bridge in
close analogy to iron cables employed to build ordinary span bridges. A
necessary condition for the construction of a water bridge is that a large
electric field exists parallel to and located within the water cable.
Presently, there is no accepted detailed theory which quantitatively explains
the forces which hold up the bridge. Our purpose is to present such theory
based on the Maxwell pressure tensor induced by the electric field albeit
within the condensed matter dielectric fluid cable.
|
0812.4845v1
|
2009-01-11
|
A Possible Theoretical Model For Studying Superconductivity In Fe-based Systems
|
A theoretical approach with a microscopic model is proposed for the observed
"high temperature superconductivity" in the Iron-based compounds. The above
scheme takes into account two important aspects viz. (i) superconducting
transition close to magnetic ordering and (ii) the layered structure. From the
calculation of the superconducting transition temperature, it is shown that in
the Fe-based superconductors the magnetic mechanism for superconductivity,
operating through the effective attractive Coulomb interaction within the
framework of the Fermi Liquid theory, is highly plausible.
|
0901.1438v1
|
2009-02-09
|
Dislocation Core Energies and Core Fields from First Principles
|
Ab initio calculations in bcc iron show that a <111> screw dislocation
induces a short-range dilatation field in addition to the Volterra elastic
field. This core field is modeled in anisotropic elastic theory using force
dipoles. The elastic modeling thus better reproduces the atom displacements
observed in ab initio calculations. Including this core field in the
computation of the elastic energy allows deriving a core energy which converges
faster with the cell size, thus leading to a result which does not depend on
the geometry of the dislocation array used for the simulation.
|
0902.1451v1
|
2009-02-21
|
Unconventional Pairing in Doped Band Insulators on a Honeycomb Lattice : the Role of the Disconnected Fermi Surface and a Possible Application to Superconducting $β$-MNCl (M=Hf,Zr)
|
We investigate the possibility of realizing unconventional superconductivity
in doped band insulators on the square lattice and the honeycomb lattice, where
the latter is found to be a good candidate due to the disconnectivity of the
Fermi surface. We propose applying the theory to the superconductivity in doped
layered nitride $\beta$-$M$NCl ($M=$Hf, Zr). Finally, we compare two groups of
superconductors with disconnected Fermi surface, $\beta$-$M$NCl and the iron
pnictides, which have high $T_c$ despite some faults against superconductivity
are present.
|
0902.3695v1
|
2009-03-02
|
Fermi surface shrinking and interband coupling in iron-based pnictides
|
Recent measurements of Fermi surface with de Haas-van Alphen oscillations in
LaFePO showed a shrinking of the Fermi pockets with respect to first-principle
LDA calculations, suggesting an energy shift of the hole and electrons bands
with respect to LDA. We show that these shifts are a natural consequence of the
strong particle-hole asymmetry of electronic bands in pnictides, and that they
provide an indirect experimental evidence of a dominant interband scattering in
these systems.
|
0903.0315v2
|
2009-03-08
|
Predictions of highest Transition-temperature for electron-phonon superconductors
|
Using the Eliashberg strong coupling theory with vertex correction, we
calculate maps of transition temperatures (T$_{c}$) of electron-phonon
superconductors in full parameter space. The maximums of transition
temperatures for superconductors are predicted based on the maps and the
criterion of instability of superconductivity. The strong vertex correction and
high transition temperature are tightly correlated in superconductors. We
predict that the maximum of T$_{c}$ of new iron-based superconductors will be
close to 90(K).
|
0903.1395v1
|
2009-03-18
|
Piezonuclear neutrons from fracturing of inert solids
|
Neutron emission measurements by means of helium-3 neutron detectors were
performed on solid test specimens during crushing failure. The materials used
were marble and granite, selected in that they present a different behaviour in
compression failure (i.e., a different brittleness index) and a different iron
content. All the test specimens were of the same size and shape. Neutron
emissions from the granite test specimens were found to be of about one order
of magnitude higher than the natural background level at the time of failure.
|
0903.3104v1
|
2009-03-26
|
SCES '08 - concluding remarks
|
This year's SCES has proved exciting in the array of unconventional phenomena
discovered both in novel systems, and by the renewed investigation of age-old
systems, arguably in the vicinity of QCPs. From heavy fermion systems, to
cuprate superconductors, and in a new twist iron pnictide superconductors -
some questions remain: just how similar or different are correlated phenomena
in these systems? Further, how ubiquitous are ultra-strongly correlated effects
such as the fractional quantum Hall effect (QHE), and can cold atom systems
mimic such correlated phases? We shall discuss some of these issues here.
|
0903.4548v1
|
2009-04-05
|
Destruction of graphene by metal adatoms
|
The formation energies for mono- and bivacancies in graphene in the presence
of adatoms of various metals and small metallic clusters have been calculated.
It is shown that transition metal impurities, such as iron, nickel and,
especially, cobalt reduce dramatically the vacancy formation energies whereas
gold impurities have almost no effect on characteristics of the vacancies. This
results highlight that special measures are required in order to protect
graphene from damage by transition metal leads.
|
0904.0807v2
|
2009-04-30
|
Preparation and superconductivity of iron selenide thin films
|
FeSex (x = 0.80, 0.84, 0.88, 0.92) thin films were prepared on SrTiO3(001)
(STO), (La,Sr)(Al,Ta)O3(001) (LSAT), and LaAlO3(001) (LAO) substrates by pulsed
laser deposition method. All thin films show single-phase and c-axis oriented
epitaxial growth, and are superconducting. Among them, the FeSe0.88 thin films
show Tc, onset of 11.8 K and Tc, 0 of 3.4 K. The upper critical magnetic field
is estimated to be 14.0 T.
|
0904.4731v1
|
2009-05-02
|
Quantum fluctuation and geometrical frustration effects on electric polarization
|
We examine theoretically a possibility of ferroelectricity caused by
electronic charge order without inversion symmetry, motivated by layered iron
oxides. Quantum electronic models in a paired-triangular lattice are analyzed
by utilizing the variational Monte Carlo simulation. Our calculation
demonstrates that combined effects of electron transfer between the layers,
corresponding to quantum fluctuation between the potential minima, and
geometrical frustration promote appearance of an electric polarization. Present
results are in contrast to the conventional manner of quantum fluctuation in
ferroelectricity.
|
0905.0182v1
|
2009-05-04
|
Berry Phase Coupling and the Cuprate Neutron Scattering Resonance
|
We examine the influence of coupling between particle-hole and
particle-particle spin fluctuations on the inelastic neutron scattering
resonance (INSR) in cuprate superconductors in both weak and strong interaction
limits. For weak-interactions in the particle-hole channel, we find that the
interchannel coupling can eliminate the resonance. For strong interactions
which drive the system close to a $\bm{Q}=(\pi,\pi)$ magnetic instablity, the
resonance frequency always approaches zero but its value is influenced by the
interchannel coupling. We comment on constraints imposed on cuprate physics by
the INSR phenomenology, and a comparison between the cuprates and the
newly-discovered iron pnictide superconductors is discussed.
|
0905.0464v1
|
2009-05-12
|
Magnetic vortex as a ground state for sub-micron antiferromagnetic particles
|
For submicron particles shaped as any axisymmetric body and made with
standard canted antiferromagnet like hematite or iron borate, the ground state
may comprise of a magnetic vortex with topologically non-trivial distribution
of the sublattice magnetization $\vec{l}$ and planar coreless vortex-like
structure for the net magnetization $\vec{M}$. For antiferromagnetic particles
in the vortex state, in addition to low-frequency modes, there are high
frequency modes with frequencies over the range of hundreds gigahertz,
including a mode localized in the region of the radius 30-40 nm near a vortex
core.
|
0905.1966v2
|
2009-05-24
|
Magnetic impurities in the two-band $s_\pm$-wave superconductors
|
We investigate the effects of magnetic impurities in a superconducting state
with $s_\pm$ pairing symmetry. Within a two-band model, we find that the
intra-band magnetic scattering serves as a pair breaker while the inter-band
magnetic scattering preserves pairing and hardly affects transition temperature
in the Born limit. We also show that the same physics can persist beyond the
weak scattering region. Our results coincide with recent experimental
measurements in iron-based superconductors and thus provides an indirect
evidence of the possible $s_\pm$ pairing symmetry in these materials.
|
0905.3883v2
|
2009-05-25
|
Electron Spin Resonance investigation of undoped and Li-doped CdWO_4 scintillator crystals
|
Electron spin resonance (ESR) spectra of Fe3+ and Mn2+ ions have been studied
in the nominally pure and 0.05% Li-doped single crystals of CdWO4. The
zero-field splitting parameters are determined with a high precision for both
of the impurities. The result suggest that the Li-doping leads to the increase
of the ionic charge of iron from 3+ to 4+ and of manganese, from 1+ to 2+.
|
0905.4011v1
|
2009-06-02
|
Enhancement of Critical Current Densities in Co-Doped BaFe$_{2}$As$_{2}$ with Columnar Defects Introduced by Heavy-Ion Irradiation
|
We report the first realization of columnar defects in Co-doped
BaFe$_{2}$As$_{2}$ single crystals by heavy-iron irradiation. The columnar
defects are confirmed by transmission electron microscopy and their density is
about 40 % of the irradiation dose. Magneto-optical imaging and bulk
magnetization measurements reveal that the critical current density is strongly
enhanced in the irradiated region. We also find that vortex creep rates are
strongly suppressed by the columnar defects. We compare the effect of heavy-ion
irradiation into Co-doped BaFe$_{2}$As$_{2}$ and cuprate superconductors.
|
0906.0444v1
|
2009-06-14
|
The Radial Dependence of Temperature and Iron Abundance: Galaxy Clusters from z=0.14 to z=0.89
|
Using archival Chandra and XMM-Newton data on 35 galaxy clusters, we measured
average temperature and metallicity profiles for clusters based separated by
temperature, cooling time, and redshift. Our results show no evidence for
significant changes in the metallicity or temperature profiles with redshift
once these selection effects are taken into account.
|
0906.2564v1
|
2009-06-22
|
Kondo resonance narrowing in d- and f-electron systems
|
By developing a simple scaling theory for the effect of Hund's interactions
on the Kondo effect, we show how an exponential narrowing of the Kondo
resonance develops in magnetic ions with large Hund's interaction. Our theory
predicts an exponential reduction of the Kondo temperature with spin S of the
Hund's coupled moment, a little-known effect first observed in d-electron
alloys in the 1960's, and more recently encountered in numerical calculations
on multi-band Hubbard models with Hund's interactions. We discuss the
consequences of Kondo resonance narrowing for the Mott transition in d-band
materials, particularly iron pnictides, and the narrow ESR linewidth recently
observed in ferromagnetically correlated f-electron materials.
|
0906.4107v1
|
2009-06-29
|
Elastic energy of a straight dislocation and contribution from core tractions
|
We derive an expression of the core traction contribution to the dislocation
elastic energy within linear anisotropic elasticity theory using the sextic
formalism. With this contribution, the elastic energy is a state variable
consistent with the work of the Peach-Koehler forces. This contribution needs
also to be considered when extracting from atomic simulations core energies.
The core energies thus obtained are real intrinsic dislocation properties: they
do not depend on the presence and position of other defects. This is
illustrated by calculating core energies of edge dislocation in bcc iron, where
we show that dislocations gliding in {110} planes are more stable than those
gliding in {112} planes.
|
0906.5332v1
|
2009-07-15
|
Perfect and partial hedging for swing game options in discrete time
|
The paper introduces and studies hedging for game (Israeli) style extension
of swing options considered as multiple exercise derivatives. Assuming that the
underlying security can be traded without restrictions we derive a formula for
valuation of multiple exercise options via classical hedging arguments.
Introducing the notion of the shortfall risk for such options we study also
partial hedging which leads to minimization of this risk.
|
0907.2541v1
|
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