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2011-09-29 | Signatures of electronic correlations in iron silicide | The intermetallic FeSi exhibits an unusual temperature dependence in its
electronic and magnetic degrees of freedom, epitomized by the crossover from a
low temperature non-magnetic semiconductor to a high temperature paramagnetic
metal with a Curie-Weiss like susceptibility. Many proposals for this
unconventional behav... | 1109.6561v2 |
2011-10-03 | Phase transitions in spin-orbital models with spin-space anisotropies for iron-pnictides: A study through Monte Carlo simulations | The common phase diagrams of superconducting iron pnictides show interesting
material specificities in the structural and magnetic phase transitions. In
some cases the two transitions are separate and second order, while in others
they appear to happen concomitantly as a single first order transition. We
explore these ... | 1110.0434v2 |
2011-10-04 | Two-orbital quantum spin model of magnetism in the iron pnictides | We study a two-orbital spin model to describe (pi,0) stripe
antiferromagnetism in the iron pnictides. The "double-spin" model has an
on-site Hunds's coupling and inter-site interactions extending to second
neighbors (inter- and intra-orbital) on the square lattice. Using a variational
method based on a cluster decompos... | 1110.0761v2 |
2011-10-14 | Interplay between spin density wave and superconductivity in '122' iron pnictides: 57Fe Mössbauer study | Iron-based superconductors Ba0.7Rb0.3Fe2As2 and CaFe1.92Co0.08As2 of the
'122' family have been investigated by means of the 14.41-keV Moessbauer
transition in 57Fe versus temperature ranging from the room temperature till
4.2 K. A comparison is made with the previously investigated parent compounds
BaFe2As2 and CaFe2A... | 1110.3170v1 |
2011-10-19 | Synthesis of novel rare earth - iron oxide chalcogenides with the La2Fe2O3Se2 structure | Our searches for new oxide chalcogenides of rare earths and Fe, Co, Ni, and
Zn resulted in preparation of two new compounds Ce2Fe2O3S2 and Pr2Fe2O3S2 which
are isostructural to La2Fe2O3Se2 and Sm2Ti2O3Sb2. Crystal structures of the new
compounds Ce2Fe2O3S2 and Pr2Fe2O3S2 were determined from powder X-ray
diffraction da... | 1110.4234v1 |
2011-10-21 | P-T phase diagram of iron arsenide superconductor NdFeAsO0.88F0.12 | NdFeAsO0.88F0.12 belongs to the recently discovered family of high-TC
iron-based superconductors. The influence of high pressure on transport
properties of this material has been studied. Contrary to La-based compounds,
we did not observe a maximum in TC under pressure. Under compression, TC drops
rapidly as a linear f... | 1110.4909v1 |
2011-10-22 | Strong field effects on emission line profiles: Kerr black holes and warped accretion disks | If an accretion disk around a black hole is illuminated by hard X-rays from
non-thermal coronae, fluorescent iron lines will be emitted from the inner
region of the accretion disk. The emission line profiles will show a variety of
strong field effects, which may be used as a probe of the spin parameter of the
black hol... | 1110.4997v1 |
2011-10-30 | Microwave Surface Impedance Measurements of the Electronic State and Dissipation of Magnetic Vortices in Superconducting Iron-Based LiFeAs Single Crystals | LiFeAs is one of the iron-based superconductors having multiple gaps with the
possible sign reversal. To clarify how those novel natures affect the energy
dissipation of magnetic vortices, we investigated the microwave surface
impedance of LiFeAs single crystals under finite magnetic fields. The flux-flow
resistivity e... | 1110.6575v2 |
2011-10-31 | Spin-dependent recombination in Czochralski silicon containing oxide precipitates | Electrically detected magnetic resonance is used to identify recombination
centers in a set of Czochralski grown silicon samples processed to contain
strained oxide precipitates with a wide range of densities (~ 1e9 cm-3 to ~
7e10 cm-3). Measurements reveal that photo-excited charge carriers recombine
through Pb0 and P... | 1110.6727v1 |
2011-10-31 | One-sign order parameter in iron based superconductor | The onset of superconductivity at the transition temperature is marked by the
onset of order, which is characterized by an energy gap. Most models of the
iron-based superconductors find a sign-changing (s\pm) order parameter [1-6],
with the physical implication that pairing is driven by spin fluctuations.
Recent work, ... | 1110.6922v2 |
2011-11-17 | Competition between commensurate and incommensurate magnetic ordering in Fe(1+y)Te | The Fe1+y Te1-x Sex compounds belong to the family of iron-based high
temperature superconductors, in which superconductivity often appears upon
doping antiferromagnetic parent compounds. Unlike other Fe-based
superconductors (in which the antiferromagnetic order is at the Fermi surface
nesting wavevector [1/2,1/2,1]),... | 1111.4236v2 |
2011-11-26 | Electronic reconstruction through the structural and magnetic transitions in detwinned NaFeAs | We use angle-resolved photoemission spectroscopy to study twinned and
detwinned iron pnictide compound NaFeAs. Distinct signatures of electronic
reconstruction are observed to occur at the structural (TS) and magnetic (TSDW)
transitions. At TS, C4 rotational symmetry is broken in the form of an
anisotropic shift of the... | 1111.6134v1 |
2011-11-29 | Suzaku Observation of the Black Hole Candidate MAXI J1836-194 in a Hard/Intermediate Spectral State | We report on a Suzaku observation of the newly discovered X-ray binary MAXI
J1836-194. The source is found to be in the hard/intermediate spectral state
and displays a clear and strong relativistically broadened iron emission line.
We fit the spectra with a variety of phenomenological, as well as physically
motivated d... | 1111.6665v3 |
2011-12-07 | Reciprocal-space structure and dispersion of the magnetic resonant mode in the superconducting phase of Rb(x)Fe(2-y)Se2 single crystals | Inelastic neutron scattering is employed to study the reciprocal-space
structure and dispersion of magnetic excitations in the normal and
superconducting states of single-crystalline Rb0.8Fe1.6Se2. We show that the
recently discovered magnetic resonant mode in this compound has a
quasi-two-dimensional character, simila... | 1112.1636v1 |
2011-12-19 | Anomalous isotope effect in phonon-dressed iron-based superconductor | The role of electron-phonon interactions in iron-based superconductor is
currently under debate with conflicting experimental reports on the isotope
effect. To address this important issue, we employ the renormalization-group
method to investigate the competition between electron-electron and
electron-phonon interactio... | 1112.4326v3 |
2011-12-20 | Do Transition Metal Substitutions Dope Carriers in Iron Based Superconductors? | We investigate the currently debated issue concerning whether transition
metal substitutions dope carriers in iron based superconductors. From
first-principles calculations of the configuration-averaged spectral function
of BaFe$_2$As$_2$ with disordered Co/Zn substitutions of Fe, important doping
effects are found bey... | 1112.4858v3 |
2011-12-30 | Structural, Magnetic and Electronic Properties of the Iron-Chalcogenide A$_x$Fe$_{2-y}$Se$_2$ (A=K, Cs, Rb, Tl and etc.) Superconductors | The latest discovery of a new iron-chalcogenide superconductor
A$_x$Fe$_{2-y}$Se$_2$(A=K, Cs, Rb, Tl and etc.) has attracted much attention
due to a number of its unique characteristics, such as the possible insulating
state of the parent compound, the existence of Fe-vacancy and its ordering, a
new form of magnetic st... | 1201.0085v1 |
2012-01-01 | Effect of transition-metal substitution in iron-based superconductors | We study theoretically the current debatable issue about the effect of
transition-metal (TM) substitution in iron-based superconductors through
treating all of the TM ions as randomly distributed impurities. The extra
electrons from TM elements are localized at the impurity sites. In the mean
time the chemical potentia... | 1201.0363v2 |
2012-01-12 | Q-scan-analysis of the neutron scattering in iron-based superconductors | We propose a way to determine the pairing state of the iron pnictide
superconductors exploiting the momentum (Q) scan of the neutron scattering
data. We investigate the spin susceptibility in the s+- and s++ superconducting
states for various doping levels using the effective five-orbital model and
considering the quas... | 1201.2453v2 |
2012-01-16 | (PI,0) antiferromagnetic spin excitations in superconducting Rb0.82Fe1.68Se2 | We use inelastic neutron scattering to show that superconducting (SC)
rubidium iron selenide Rb0.82Fe1.68Se2 exhibits antiferromagnetic (AF) spin
excitations near the in-plane wave vector Q = (PI, 0) identical to that for
iron arsenide superconductors. Moreover, we find that these excitations change
from incommensurate... | 1201.3348v1 |
2012-01-20 | Non-destructive imaging of an individual protein | The mode of action of proteins is to a large extent given by their ability to
adopt different conformations. This is why imaging single biomolecules at
atomic resolution is one of the ultimate goals of biophysics and structural
biology. The existing protein database has emerged from X-ray crystallography,
NMR or cryo-T... | 1201.4300v1 |
2012-01-25 | Pressure Effects on Magnetically-Driven Electronic Nematic States in Iron-Pnictides | In a magnetically driven electronic nematic state, an externally applied
uniaxial strain rounds the nematic transition and increases the magnetic
transition temperature. We study both effects in a simple classical model of
the iron-pnictides expressed in terms of local SO(N) spins (with N = 3) which
we solve to leading... | 1201.5174v1 |
2012-02-01 | 120-mm superconducting quadrupole for interaction regions of hadron colliders | Magnetic and mechanical designs of a Nb3Sn quadrupole magnet with 120-mm
aperture suitable for interaction regions of hadron colliders are presented.
The magnet is based on a two-layer shell-type coil and a cold iron yoke.
Special spacers made of a low-Z material are implemented in the coil mid-planes
to reduce the lev... | 1202.0293v1 |
2012-02-03 | Gap opening and orbital modification of superconducting FeSe above the structural distortion | We utilize steady-state and transient optical spectroscopies to examine the
responses of nonthermal quasiparticles with respect to orbital modifications in
normal-state iron-chalcogenide superconductors. The dynamics shows the
emergence of gap-like quasiparticles (associated to a ~36 meV energy gap) with
a coincident t... | 1202.0658v1 |
2012-02-08 | Pairing Symmetry and Spin Excitations of Iron Selenide Superconductors | We propose an effective single-band model for the newly discovered iron
selenide superconductors A$_x$Fe$_{2-y}$Se$_2$ (A=Tl,K,Rb,Cs). Based on this
minimum model and the random phase approximation, the $d_{x^2-y^2}$ pairing
symmetry is revealed theoretically, which may be understood in the framework of
Fermi surface t... | 1202.1607v1 |
2012-02-16 | Transport and magnetic properties of La-doped CaFe$_2$As$_2$ | We measured the transport properties and susceptibility of single crystals
Ca$_{1-x}$La$_x$Fe$_2$As$_2$(x=0, 0.05, 0.1, 0.15, 0.19 and 0.25). Large
in-plane resistivity anisotropy similar to that in Co-doped 122 iron-pnictides
is observed although no transition metals were introduced in the FeAs-plane.
The in-plane res... | 1202.3589v1 |
2012-02-20 | Sign-reversal of the in-plane resistivity anisotropy in hole-doped iron pnictides | The in-plane anisotropy of the electrical resistivity across the coupled
orthorhombic and magnetic transitions of the iron pnictides has been
extensively studied in the parent and electron-doped compounds. All these
studies universally show that the resistivity $\rho_{a}$ across the long
orthorhombic axis $a_{O}$ - alo... | 1202.4430v2 |
2012-03-05 | Gap nodes induced by coexistence with antiferromagnetism in iron-based superconductors | We investigate the pairing in iron pnictides in the coexistence phase, which
displays both superconducting and antiferromagnetic orders. By solving the
pairing problem on the Fermi surface reconstructed by long-range magnetic
order, we find that the pairing interaction necessarily becomes
angle-dependent, even if it wa... | 1203.0991v1 |
2012-03-06 | Nanoscale Metallic Iron for Environmental Remediation: Prospects and Limitations | The amendment of the subsurface with nanoscale metallic iron particles
(nano-Fe0) has been discussed in the literature as an efficient in situ
technology for groundwater remediation. However, the introduction of this
technology was controversial and its efficiency has never been univocally
established. This unsatisfyin... | 1203.1128v1 |
2012-03-08 | NMR Study in the Iron-Selenide Rb0.74Fe1.6Se2: Determination of the Superconducting Phase as Iron Vacancy-Free Rb0.3Fe2Se2 | 77Se and 87Rb nuclear magnetic resonance (NMR) experiments on Rb0.74Fe1.6Se2
reveal clearly distinct spectra originating from a majority antiferromagnetic
(AF) and a minority metallic-superconducting (SC) phase. The very narrow NMR
line of the SC phase evidences the absence of Fe vacancies and any trace of AF
order. Th... | 1203.1834v2 |
2012-03-08 | Simulation of proton-induced and iron-induced extensive air showers at extreme energies | The development of extensive air showers at extreme energies is studied using
a simulation model much simpler and cruder, but also more transparent and
flexible, than existing sophisticated codes. Evidence for its satisfactory
performance is presented. As an illustration, shower elongation rates are
evaluated in the $1... | 1203.1845v1 |
2012-03-13 | Self-Consistent Vertex Correction Analysis for Iron-Based Superconductors: Mechanism of Coulomb-Interaction-Driven Orbital Fluctuations | We study the mechanism of orbital/spin fluctuations due to multiorbital
Coulomb interaction in iron-based superconductors, going beyond the
random-phase-approximation. For this purpose, we develop a self-consistent
vertex correction (SC-VC) method, and find that multiple orbital fluctuations
in addition to spin fluctua... | 1203.2874v3 |
2012-03-16 | Interstellar polarization and grain alignment: the role of iron and silicon | We compiled the polarimetric data for a sample of lines of sight with known
abundances of Mg, Si, and Fe. We correlated the degree of interstellar
polarization $P$ and polarization efficiency (the ratio of $P$ to the colour
excess $E(B-V)$ or extinction $A_V$) with dust phase abundances. We detect an
anticorrelation be... | 1203.3677v1 |
2012-03-19 | Photoionization Cross-Sections for the trans-iron element Se$^+$ from 18 eV to 31 eV | Absolute photoionization cross-section calculations are presented for Se$^+$
using large-scale close-coupling calculations within the Breit-Pauli and
Dirac-Coulomb R-matrix approximations. The results from our theoretical work
are compared with recent measurements made at the Advanced Light Source (ALS)
radiation facil... | 1203.4102v1 |
2012-03-21 | Non-Fermi-Liquid Transport Phenomena and Superconductivity Driven by Orbital Fluctuations in Iron Pnictides: Analysis by Fluctuation-Exchange Approximation | We study the five-orbital Hubbard model including the charge quadrupole
interaction for iron pnictides. Using the fluctuation-exchange (FLEX)
approximation, orbital fluctuations evolve inversely proportional to the
temperature, and therefore the resistivity shows linear or convex T-dependence
for wide range of temperat... | 1203.4639v2 |
2012-03-22 | Universal pair-breaking in transition metal-substituted iron-pnictide superconductors | The experimental transport scattering rate was determined for a wide range of
optimally doped transition metal-substituted FeAs-based compounds with the
ThCr2Si2 (122) crystal structure. The maximum transition temperature Tc for
several Ba-, Sr-, and Ca-based 122 systems follows a universal rate of
suppression with inc... | 1203.5114v3 |
2012-04-07 | KFe_2Se_2 is the parent compound of K-doped iron selenide superconductors | We elucidate the existing controversies in the newly discovered K-doped iron
selenide (KxFe2-ySe2-z) superconductors. The stoichiometric KFe2Se2 with
\surd2\times\surd2 charge ordering was identified as the parent compound of
KxFe2-ySe2-z superconductor using scanning tunneling microscopy and
spectroscopy. The supercon... | 1204.1588v1 |
2012-04-08 | Vie Physarale: Evaluation of Roman roads with slime mould | Roman Empire is renowned for sharp logical design and outstanding building
quality of its road system. Many roads built by Romans are still use in
continental Europe and UK. The Roman roads were built for military
transportations with efficiency in mind, as straight as possible. Thus the
roads make an ideal test-bed fo... | 1204.2260v1 |
2012-04-10 | The symplectic-N t-J model and s$_\pm$ superconductors | The possible discovery of $s_\pm$ superconducting gaps in the moderately
correlated iron-based superconductors has raised the question of how to
properly treat $s_\pm$ gaps in strongly correlated superconductors. Unlike the
d-wave cuprates, the Coulomb repulsion does not vanish by symmetry, and a
careful treatment is e... | 1204.2302v2 |
2012-04-18 | Electronic properties and magnetism of iron at the Earth's inner core conditions | We employ state-of-the-art ab initio simulations within the dynamical
mean-field theory to study three likely phases of iron (hexogonal close-packed,
hcp, face centered cubic, fcc, and body centered cubic, bcc) at the Earth's
core conditions. We demonstrate that the correction to the electronic free
energy due to corre... | 1204.3954v2 |
2012-04-19 | Paramagnetic Phase of a Heavy-Fermion Compound, CeFePO, Probed by 57Fe Mössbauer Spectroscopy | 57Fe M\"{o}ssbauer spectroscopy was applied to an iron-based layered compound
CeFePO. At temperatures from 9.4 to 293 K, no magnetic splitting was observed
in the M\"ossbauer spectra of CeFePO indicating a paramagnetic phase of the Fe
magnetic sublattice. All the spectra were fitted with a small quadrupole
splitting, a... | 1204.4266v1 |
2012-04-25 | Susceptibility anisotropy in an iron arsenide superconductor revealed by x-ray diffraction in pulsed magnetic fields | In addition to unconventional high-Tc superconductivity, the iron arsenides
exhibit strong magnetoelastic coupling and a notable electronic anisotropy
within the a-b plane. We relate these properties by studying underdoped
Ba(Fe{1-x}Co{x})2As2 by x-ray diffraction in pulsed magnetic fields up to 27.5
Tesla. We exploit ... | 1204.5693v1 |
2012-05-08 | X-Ray view of Misaligned AGNs | The Fermi-LAT satellite has recently discovered a small group of radio
galaxies and steep spectrum radio sources: the misaligned AGNs (MAGNs) sample.
We present the X-ray analysis of all the sources of this sample (7 FRIs and 3
FRIIs) with a firm GeV association. This study supports the idea that FRIIs
host more effici... | 1205.1691v1 |
2012-05-08 | Short-range symmetry breaking induced structural collapse and Tc enhancement in 122-type iron pnictide superconductors | In this paper, we investigate analytically the experimental observations of
structural collapse and Tc enhancement in the rare earth-doped 122-type
iron-based pnictide superconductors [S. R. Saha et.al. Phys. Rev. B 85, 024525
(2012), arXiv:1105.4798 (2011); B. Lv et al. PNAS 108, 15705 (2011).]. Based on
the real-spac... | 1205.1837v1 |
2012-05-11 | Theory of Mixed-State Effect on Quasiparticle Interference in Iron-based Superconductors | Based on a phenomenological model with $s_{\pm}$ or s-wave pairing symmetry,
the mixed-state effect on quasiparticle interference in iron-based
superconductors is investigated by solving large-scale Bogoliubov-de Gennes
equations based on the Chebyshev polynomial expansion. Taking into account the
presence of magnetic ... | 1205.2418v1 |
2012-05-23 | Breaking of four-fold lattice symmetry in a model for pnictide superconductors | We investigate the interplay of onsite Coulomb repulsion and various
mechanisms breaking the fourfold lattice symmetry in a three-band model for the
iron planes of iron-based superconductors. Using cluster-perturbation theory
allows us to locally break the symmetry between the x- and y-directions without
imposing long-... | 1205.5102v1 |
2012-05-27 | The Topological Relation Between Bulk Gap Nodes and Surface Bound States : Application to Iron-based Superconductors | In the past few years materials with protected gapless surface (edge) states
have risen to the central stage of condensed matter physics. Almost all
discussions centered around topological insulators and superconductors, which
possess full quasiparticle gaps in the bulk. In this paper we argue systems
with topological ... | 1205.5933v3 |
2012-05-30 | New Phase Induced by Pressure in the Iron-Arsenide Superconductor K-Ba122 | The electrical resistivity rho of the iron-arsenide superconductor
Ba1-xKxFe2As2 was measured in applied pressures up to 2.6 GPa for four
underdoped samples, with x = 0.16, 0.18, 0.19 and 0.21. The antiferromagnetic
ordering temperature T_N, detected as a sharp anomaly in rho(T), decreases
linearly with pressure. At pr... | 1205.6730v2 |
2012-05-30 | The Submm and mm Excess of the SMC: Magnetic Dipole Emission from Magnetic Nanoparticles? | The Small Magellanic Cloud (SMC) has surprisingly strong submm and
mm-wavelength emission that is inconsistent with standard dust models,
including those with emission from spinning dust. Here we show that the
emission from the SMC may be understood if the interstellar dust mixture
includes magnetic nanoparticles, emit... | 1205.6810v1 |
2012-06-02 | Effect of substitution and heat treatment route on polycrystalline FeSe0.5Te0.5 Superconductors | The effect of atomic substitution of Te in iron based superconductors FeSe
(1:1 type), which exhibits the simplest crystal structure among the iron-based
superconductors, has been investigated in terms of structural, electronic
transport and magnetic properties. Polycrystalline samples with nominal Se:Te
in FeSe1-xTex ... | 1206.0401v2 |
2012-06-05 | Fractional power-law behavior and its origin in iron-chalcogenide and ruthenate superconductors: Insights from first-principles calculations | We perform realistic first-principles calculations of iron chalcogenides and
ruthenate based materials to identify experimental signatures of Hund's
coupling induced correlations in these systems. We find that FeTe and
K$_x$Fe$_{2-y}$Se$_2$ display unusual orbital dependent fractional powerlaw
behavior in their quasipa... | 1206.0801v3 |
2012-06-08 | Studies of concentration and temperature dependencies of precipitation kinetics in iron-copper alloys using kinetic monte carlo and stochastic statistical simulations | The earlier-developed ab initio model and the kinetic Monte Carlo method
(KMCM) are used to simulate precipitation in a number of iron-copper alloys
with different copper concentrations x and temperatures T. The same simulations
are also made using the improved version of the earlier-suggested stochastic
statistical me... | 1206.1792v1 |
2012-06-12 | Density functional theory calculations and vibrational spectroscopy on iron spin-crossover compounds | Iron complexes with a suitable ligand field undergo spin-crossover (SCO),
which can be induced reversibly by temperature, pressure or even light.
Therefore, these compounds are highly interesting candidates for optical
information storage, for display devices and pressure sensors. The SCO
phenomenon can be conveniently... | 1206.2469v1 |
2012-06-13 | Dynamics of Metal Centers Monitored by Nuclear Inelastic Scattering | Nuclear inelastic scattering of synchrotron radiation has been used now since
10 years as a tool for vibrational spectroscopy. This method has turned out
especially useful in case of large molecules that contain a M\"ossbauer active
metal center. Recent applications to iron-sulfur proteins, to iron(II) spin
crossover c... | 1206.2760v1 |
2012-06-25 | Structure and physical properties of new layered iron oxychalcogenide BaFe2OSe2 | We have successfully synthesized a new layered iron oxychalcogenide BaFe2OSe2
single crystal. This compound is built up of Ba and Fe-Se(O) layers
alternatively stacked along the c-axis. The Fe-Se(O) layers contain double
chains of edge-shared Fe-Se(O) tetrahedra that propagate along the b-axis and
are bridged by oxygen... | 1206.5788v1 |
2012-06-29 | Synthesis of a new alkali metal-organic solvent intercalated iron selenide superconductor with Tc{\approx}45K | We report on a new iron selenide superconductor with a TC onset of 45K and
the nominal composition Lix(C5H5N)yFe2-zSe2, synthesized via intercalation of
dissolved alkaline metal in anhydrous pyridine at room temperature. This
superconductor exhibits a broad transition, reaching zero resistance at 10K.
Magnetization mea... | 1206.7022v1 |
2012-07-09 | Multifractal scaling of flux penetration in the Iron-based Superconductor Ba(Fe$_{0.93}$Co$_{0.07}$)$_{2}$As$_2$ | The penetration of magnetic flux fronts in the optimally-doped iron-based
superconductor Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_2$ ($x = 0.07 \pm 0.005$) is
studied by means of magneto-optical imaging and Bitter decoration. The
higher-order analysis of roughening and growth of the magnetic flux front
reveals anomalous scaling... | 1207.2068v2 |
2012-07-10 | Optical properties of the iron-pnictide analog BaMn2As2 | We have investigated the infrared and Raman optical properties of BaMn2As2 in
the ab-plane and along the c-axis. The most prominent features in the infrared
spectra are the Eu and A2u phonon modes which show clear TO-LO splitting from
the energy loss function analysis. All the phonon features we observed in
infrared an... | 1207.2360v1 |
2012-07-10 | NLTE line formation of Fe in late-type stars II: 1D spectroscopic stellar parameters | We investigate departures from local thermodynamic equilibrium (NLTE) in the
line formation of neutral and singly ionised iron lines and their impact on
spectroscopic stellar parameters. The calculations are performed for an
extensive grid of 1D MARCS models of metal-rich and metal-poor late-type dwarfs
and giants. We ... | 1207.2454v1 |
2012-07-12 | Strong electronic correlations from Hund's coupling | Strong electronic correlations are often associated with the proximity of a
Mott insulating state. In recent years however, it has become increasingly
clear that the Hund's rule coupling (intra-atomic exchange) is responsible for
strong correlations in multi-orbital metallic materials which are not close to
a Mott insu... | 1207.3033v2 |
2012-07-13 | Investigation of the Superconducting Gap Structure in SrFe$_2$(As$_{0.7}$P$_{0.3}$)$_2$ by Magnetic Penetration Depth and Flux Flow Resistivity Analysis | We measured the microwave surface impedances and obtained the superfluid
density and flux flow resistivity in single crystals of a phosphor-doped
iron-based superconductor SrFe$_2$(As$_{1-x}$P$_{x}$)$_2$ single crystals
($x=0.30$, $T_c=25 \mathrm{K}$). At low temperatures, the superfluid density,
$n_s (T)/n_s(0)$, obey... | 1207.3155v1 |
2012-07-26 | High pressure transport studies of the LiFeAs analogues CuFeTe2 and Fe2As | We have synthesized two iron-pnictide/chalcogenide materials, CuFeTe2 and
Fe2As, which share crystallographic features with known iron-based
superconductors, and carried out high-pressure electrical resistivity
measurements on these materials to pressures in excess of 30 GPa. Both
compounds crystallize in the Cu2Sb-typ... | 1207.6272v1 |
2012-07-29 | Oriented gap opening in the magnetically ordered state of Iron-pnicitides: an impact of intrinsic unit cell doubling on the $Fe$ square lattice by $As$ atoms | We show that the complicated band reconstruction near Fermi surfaces in the
magnetically ordered state of iron-pnictides observed by angle-resolved
photoemission spectroscopies (ARPES) can be understood in a meanfield level if
the \emph{intrinsic unit cell doubling} due to As atoms is properly considered
as shown in th... | 1207.6798v1 |
2012-07-30 | Surface adatom conductance filtering in scanning tunneling spectroscopy of Co-doped BaFe2As2 iron pnictide superconductors | We establish in a combination of ab initio theory and experiments that the
tunneling process in scanning tunneling microscopy/spectroscopy on the A-122
iron pnictide superconductors - in this case BaFe$_{2-x}$Co$_x$As$_2$ - involve
a strong adatom filtering of the differential conductance from the near-EF Fe3d
states, ... | 1207.7122v1 |
2012-08-06 | Superconductivity in striped and multi-Fermi-surface Hubbard models: From the cuprates to the pnictides | Single- and multi-band Hubbard models have been found to describe many of the
complex phenomena that are observed in the cuprate and iron-based
high-temperature superconductors. Simulations of these models therefore provide
an ideal framework to study and understand the superconducting properties of
these systems and t... | 1208.1158v1 |
2012-08-09 | Orbital differentiation and the role of orbital ordering in the magnetic state of Fe superconductors | We analyze the metallic (pi,0) antiferromagnetic state of a five-orbital
model for iron superconductors. We find that with increasing interactions the
system does not evolve trivially from the pure itinerant to the pure localized
regime. Instead we find a region with a strong orbital differentiation between
xy and yz, ... | 1208.1917v2 |
2012-08-10 | Effective medium approximation and the complex optical properties of the inhomogeneous superconductor K_{0.8}Fe_{2-y}Se_2 | The in-plane optical properties of the inhomogeneous iron-chalcogenide
superconductor K_{0.8}Fe_{2-y}Se_2 with a critical temperature Tc = 31 K have
been modeled in the normal state using the Bruggeman effective medium
approximation for metallic inclusions in an insulating matrix. The volume
fraction for the inclusions... | 1208.2240v2 |
2012-08-14 | Nematicity from mixed S_{+-} + d_{x^2-y^2} states in iron-based superconductors | We demonstrate that in iron-based superconductors, the extended S_{+-} SC
state coexists with the d_{x^2-y^2} state under generic conditions. The mixed
S_{+-} + d_{x^2-y^2} SC is a natural nematic state in which the tetragonal
symmetry C_4 is broken to C_2 explaining puzzling findings of nematic SC in
FeSe films [Scien... | 1208.2881v3 |
2012-08-16 | Suppression of superconductivity by Neel-type magnetic fluctuations in the iron pnictides | Motivated by recent experimental detection of Neel-type ($(\pi,\pi)$)
magnetic fluctuations in some iron pnictides, we study the impact of competing
$(\pi,\pi)$ and $(\pi,0)$ spin fluctuations on the superconductivity of these
materials. We show that, counter-intuitively, even short-range, weak Neel
fluctuations strong... | 1208.3412v2 |
2012-08-18 | On the dual role of the d-electrons in iron-pnictides | In the stoichiometric Fe-pnictides the same d-electrons form the local
moments and participate in the metallic conductivity. In the manuscript the
emergence of the magnetic moments on the Fe-sites, their interaction with the
itinerant electrons are studied in the paramagnetic phase at the different
relations between th... | 1208.3740v2 |
2012-08-19 | A Model of the Cellular Iron Homeostasis Network Using Semi-Formal Methods for Parameter Space Exploration | This paper presents a novel framework for the modeling of biological
networks. It makes use of recent tools analyzing the robust satisfaction of
properties of (hybrid) dynamical systems. The main challenge of this approach
as applied to biological systems is to get access to the relevant parameter
sets despite gaps in ... | 1208.3851v1 |
2012-08-24 | Raman-Scattering Detection of Nearly Degenerate $s$-Wave and $d$-Wave Pairing Channels in Iron-Based Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ and Rb$_{0.8}$Fe$_{1.6}$Se$_2$ Superconductors | We show that electronic Raman scattering affords a window into the essential
properties of the pairing potential $V_{\mathbf{k},\mathbf{k^{\prime}}}$ of
iron-based superconductors. In Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ we observe band
dependent energy gaps along with excitonic Bardasis-Schrieffer modes
characterizing, res... | 1208.5006v2 |
2012-08-29 | Quantum Oscillations in Iron Pnictide Superconductors | Insight into the electronic structure of the pnictide family of
superconductors is obtained from quantum oscillation measurements. Here we
review experimental quantum oscillation data that reveal a transformation from
large quasi-two dimensional electron and hole cylinders in the paramagnetic
overdoped members of the p... | 1208.5862v1 |
2012-09-01 | Iron based superconductors: magnetism, superconductivity and electronic structure | Angle resolved photoemission spectroscopy (ARPES) reveals the features of the
electronic structure of quasi-two-dimensional crystals, which are crucial for
the formation of spin and charge ordering and determine the mechanisms of
electron-electron interaction, including the superconducting pairing. The newly
discovered... | 1209.0140v1 |
2012-09-03 | Magnetism and its microscopic origin in iron-based high-temperature superconductors | High-temperature superconductivity in the iron-based materials emerges from,
or sometimes coexists with, their metallic or insulating parent compound
states. This is surprising since these undoped states display dramatically
different antiferromagnetic (AF) spin arrangements and N$\rm \acute{e}$el
temperatures. Althoug... | 1209.0381v1 |
2012-09-06 | The role of 245 phase in alkaline iron selenide superconductors revealed by high pressure studies | Here we show that a pressure of about 8 GPa suppresses both the vacancy order
and the insulating phase, and a further increase of the pressure to about 18
GPa induces a second transition or crossover. No superconductivity has been
found in compressed insulating 245 phase. The metallic phase in the
intermediate pressure... | 1209.1340v2 |
2012-09-10 | Anisotropic but nodeless superconducting gap in the presence of spin density wave in iron-pnictide superconductor NaFe1-xCoxAs | The coexisting regime of spin density wave (SDW) and superconductivity in the
iron pnictides represents a novel ground state. We have performed high
resolution angle-resolved photoemission measurements on NaFe1-xCoxAs (x =
0.0175) in this regime and revealed its distinctive electronic structure, which
provides some mic... | 1209.1967v2 |
2012-09-14 | Acoustic and optical phonon dynamics from femtosecond time-resolved optical spectroscopy of superconducting iron pnictide Ca(Fe_0.944Co_0.056)_2As_2 | We report temperature evolution of coherently excited acoustic and optical
phonon dynamics in superconducting iron pnictide single crystal
Ca(Fe_0.944Co_0.056)_2As_2 across the spin density wave transition at T_SDW ~
85 K and superconducting transition at T_SC ~20 K. Strain pulse propagation
model applied to the genera... | 1209.3174v2 |
2012-09-22 | Dynamical Mean-Field Study of Local Pairing Interaction Mediated by Spin and Orbital Fluctuations in Iron Pnictide Superconductors | We investigate the two-orbital Hubbard model, which reproduces the electron
and hole Fermi surfaces in the iron pnictide superconductors, in the presence
of the Jahn-Teller electron-phonon coupling by using the dynamical mean-field
theory. When the intra- and inter-orbital Coulomb interactions, $U$ and $U'$,
increase w... | 1209.4954v2 |
2012-09-24 | Magnetic phase separation and superfluid density measurements in alkali metal-organic solvent intercalated iron selenide superconductor Lix(C5H5N)yFe2-zSe2 | We report the low-temperature electronic and magnetic properties of the
alkali metal-organic solvent intercalated iron selenide superconductor
Lix(C5H5N)yFe2-zSe using muon-spin-spectroscopy measurements. The zero-field
\muSR results indicate that nearly half of the sample is magnetically ordered
and there is a spatial... | 1209.5279v1 |
2012-09-24 | Ba1-xNaxTi2Sb2O (0.0 <= x <= 0.33): A Layered Titanium-based Pnictide Oxide Superconductor | A new layered Ti-based pnictide oxide superconductor, Ba1-xNaxTi2Sb2O (0.0 <=
x <= 0.33), is reported. X-ray studies reveal it crystallizes in the tetragonal
CeCr2Si2C structure. The undoped parent compound, BaTi2Sb2O (P4/mmm;
a=4.1196(1){\AA}; c=8.0951(2){\AA}), exhibits a CDW/SDW transition at 54K. Upon
chemical dopi... | 1209.5447v2 |
2012-09-27 | Oxygen Reduction Activity of Carbon Nitride Supported on Carbon Nanotubes | Fuel cells offer an alternative to burning fossil fuels, but use platinum as
a catalyst which is expensive and scarce. Cheap, alternative catalysts could
enable fuel cells to become serious contenders in the green energy sector. One
promising class of catalyst for electrochemical oxygen reduction is
iron-containing, na... | 1209.6112v1 |
2012-09-27 | Temperature dependence of the paramagnetic spin excitations in BaFe$_2$As$_2$ | We use inelastic neutron scattering to study temperature dependence of the
paramagnetic spin excitations in iron pnictide BaFe$_2$As$_2$ throughout the
Brillouin zone. In contrast to a conventional local moment Heisenberg system,
where paramagnetic spin excitations are expected to have a Lorentzian function
centered at... | 1209.6271v1 |
2012-10-01 | The distinct in-plane resistivity anisotropy in the nematic states of detwinned NaFeAs and FeTe single crystals: evidences for Hund's rule metal | The in-plane resistivity anisotropy has been studied with the Montgomery
method on two detwinned parent compounds of the iron-based superconductors,
NaFeAs and FeTe. For NaFeAs, the resistivity in the antiferromagnetic (AFM)
direction is smaller than that in the ferromagnetic (FM) direction, similar to
that observed in... | 1210.0397v1 |
2012-10-02 | Magnetism of iron and nickel from rotationally invariant Hirsch-Fye quantum Monte Carlo calculations | We present a rotationally invariant Hirsch-Fye quantum Monte Carlo algorithm
in which the spin rotational invariance of Hund's exchange is approximated by
averaging over all possible directions of the spin quantization axis. We employ
this technique to perform benchmark calculations for the two- and three-band
Hubbard ... | 1210.0911v3 |
2012-10-09 | Indirect evidence for strong coupling superconductivity in FeSe under pressure from first-principle calculations | Whether the pairing mechanism for superconductivity in iron-based
superconductors is of itinerant or local character is a question still debated
on. In order to investigate the influence of Fermi surface nesting, we
calculate from first-principles the static susceptibility of FeSe under applied
pressures, both hydrosta... | 1210.2593v1 |
2012-10-19 | Non-collinear magnetic ordering in compressed FePd$_3$ ordered alloy: a first principles study | By means of ab initio calculations based on the density functional theory we
investigated magnetic phase diagram of ordered FePd$_3$ alloy as a function of
external pressure.
Considering several magnetic configurations we concluded that the system
under pressure has a tendency to non-collinear spin alignment. Analysi... | 1210.5478v2 |
2012-11-08 | Orbital Selectivity in Hund's metals: The Iron Chalcogenides | We show that electron correlations lead to a bad metallic state in
chalcogenides FeSe and FeTe despite the intermediate value of the Hubbard
repulsion $U$ and Hund's rule coupling $J$. The evolution of the quasi particle
weight $Z$ as a function of the interaction terms reveals a clear crossover at
$U \simeq$ 2.5 eV. I... | 1211.2015v1 |
2012-11-12 | Spectral effects simulation with two-dimensional magnetohydrodynamic models of the solar photosphere | To study the structure of spatially unresolved features of the solar
photosphere, we calculated the Stokes profiles of seven photospheric iron lines
using two-dimensional nonstationary MHD models of solar granulation for various
amounts of magnetic flux (0, 10, 20, 30 mT). We investigate variations in the
absolute wave... | 1211.2791v1 |
2012-11-19 | Electronic band structure and momentum dependence of the superconducting gap in (Ca, Na)Fe2As2 from angle-resolved photoemission spectroscopy | Electronic structure of newly synthesized single crystals of calcium iron
arsenide doped with sodium with Tc ranging from 33 to 14 K has been determined
by angle-resolved photoemission spectroscopy (ARPES). The measured band
dispersion is in general agreement with theoretical calculations, nonetheless
implies absence o... | 1211.4593v1 |
2012-11-20 | Transport properties for liquid silicon-oxygen-iron mixtures at Earth's core conditions | We report on the thermal and electrical conductivities of two liquid
silicon-oxygen-iron mixtures (Fe$_{0.82}$Si$_{0.10}$O$_{0.08}$ and
Fe$_{0.79}$Si$_{0.08}$O$_{0.13}$), representative of the composition of the
Earth's outer core at the relevant pressure-temperature conditions, obtained
from density functional theory ... | 1211.4718v1 |
2012-11-26 | The nature of high-energy radiation damage in iron: Modeling results | Understanding and predicting a material's performance in response to
high-energy radiation damage, as well as designing future materials to be used
in intense radiation environments, requires the knowledge of the structure,
morphology and amount of radiation-induced structural change. We report the
results of molecular... | 1211.6147v1 |
2012-11-30 | Sensitivity of the r-process to nuclear masses | The rapid neutron capture process (r-process) is thought to be responsible
for the creation of more than half of all elements beyond iron. The scientific
challenges to understanding the origin of the heavy elements beyond iron lie in
both the uncertainties associated with astrophysical conditions that are needed
to all... | 1211.7310v1 |
2012-11-30 | Paramagnetic spin excitations in insulating Rb$_{0.8}$Fe$_{1.6}$Se$_2$ | We use neutron scattering to study temperature dependent spin excitations in
insulating antiferromagnetic (AF) Rb$_{0.8}$Fe$_{1.6}$Se$_2$. In the
low-temperature AF state, spin waves can be accurately described by a local
moment Heisenberg Hamiltonian. On warming to around the Neel temperature of
T_N=500$ K, low-energy... | 1211.7328v1 |
2012-12-04 | Growth, Characterization, Vortex Pinning and Vortex Flow Properties of Single Crystals of Iron Chalcogenide Superconductor FeCr$_{0.02}$Se | We report the growth and characterization of single crystals of iron
chalcogenide superconductor FeCr$_{0.02}$Se. There is an enhancement of the
superconducting transition temperature (T$_{\rm c}$) as compared to the T$_{\rm
c}$ of the single crystals of the parent compound Fe$_{1+x}$Se by about 25%.
The superconductin... | 1212.0814v2 |
2012-12-06 | Quantum transport modeling of Fe/MgO/Fe magnetic tunnel junction with FeO$_{0.5}$ buffer layer: the effects of correlations | We report \textit{ab initio} simulations of quantum transport properties of
Fe/MgO/Fe trilayer structures with FeO$_{0.5}$ buffer iron oxide layer, where
on-site Coulomb interaction is explicitly taken into account by local density
approximation + Hubbard \textit{U} approach. We show that on-site Coulomb
repulsion in t... | 1212.1374v1 |
2012-12-19 | Optical conductivity and Raman scattering of iron superconductors | We discuss how to analyze the optical conductivity and Raman spectra of
multi-orbital systems using the velocity and the Raman vertices in a similar
way Raman vertices were used to disentangle nodal and antinodal regions in
cuprates. We apply this method to iron superconductors in the magnetic and
non-magnetic states, ... | 1212.4765v2 |
2013-01-09 | Power-law Temperature Dependent Hall Angle in the Normal State and its Correlation with Superconductivity in iron-pnictides | We report Hall measurement of the normal state in K- and Co-doped
BaFe$_2$As$_2$, as well NaFe$_{1-x}$Co$_x$As. We found that a power-law
temperature dependence of Hall angle, cot$\theta_{\rm H}$$\propto$ $T^\beta$,
prevails in normal state with temperature range well above the structural,
spin-density-wave and superco... | 1301.1734v1 |
2013-01-09 | Interplay between lattice and spin states degree of freedom in the FeSe superconductor: dynamic spin state instabilities | Polarized Raman-scattering spectra of superconducting, single-crystalline
FeSe evidence pronounced phonon anomalies with temperature reduction. A large
6.5% hardening of the B_1g(Fe) phonon mode is attributed to the suppression of
local fluctuations of the iron spin state with the gradual decrease of the iron
paramagne... | 1301.1960v1 |
2013-01-14 | Pressure-Induced Superconductivity and Its Scaling with Doping-Induced Superconductivity in the Iron Pnictide with Skutterudite Intermediary Layers | The Ca10(PtnAs8)(Fe2As2)5 (n=3,4) compounds are a new type of iron pnictide
superconductors whose structures consist of stacking Ca-PtnAs8-Ca-Fe2As2 layers
in a unit cell. When n=3 (the 10-3-8 phase), the undoped compound is an
antiferromagnetic (AFM) semiconductor, while, when n=4 (the 10-4-8 phase), the
undoped compo... | 1301.2863v2 |
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